December-Wet/Stormy New Years Eve Ahead

[djjordan]

I'm hoping for a change for sure. My kids and I are heading up to Michigan to hopefully frolic in the snow for Christmas. Of course...they need snow first though lol.

[Portastorm]

Those 11-15 day temperature anamolies from the 6z GFS operational run sure look chilly!

[srainhoutx]

Those 11-15 day temperature anamolies from the 6z GFS operational run sure look chilly!

One can see the change already begin to show up in the 00Z Euro Ensembles as well. Confidence continues to build that wholesale pattern change is in the works near mid December.

[srainhoutx]

A bit different view of the 12Z Operational GFS North Pacific 500mb chart suggest a stout +PNA developing offshore of the West Coast pumping a ridge N into the Aleutian Islands/near or just E of the Bering Sea. A deep trough begins to develop into the Intermountain West suggesting that very cold air that has been bottled up in Western Canada will become dislodged and head S into the Plains. Also of note is a raging Polar jet with embedded short wave energy digging into the Great Basin.

Switching back to the North American 850mb view, one can see the cold air spilling S and a Pacific Tropical connection develop providing over running moisture over a chilly surface air mass. The trends continue to suggest that after we get beyond next weekend, we may well change to a much colder pattern and I would not be surprised to see a fairly significant Winter Storm develop across the Plains providing for less air mass modification and just perhaps laying some snow cover down. We will see.

[srainhoutx]

NWS Tulsa this afternoon:

ALTHOUGH ACCURACY IN LONGER TERM FORECASTING LEAVES A LOT TO BE
DESIRED... WILL MENTION SOMETHING THAT HAS CONTINUED TO APPEAR IN
THE GFS OF LATE AND IS NOW BECOMING APPARENT IN THE ECMWF. PROJECTED
NORTH AMERICAN AIR MASS MOVEMENTS ARE HINTING AT A TRUE WINTER TYPE
ARCTIC AIR MASS SWEEPING DOWN THE PLAINS ON ABOUT DAY 10 OR 11. IT
IS TOO SOON TO EVEN GUESS WHETHER SIGNIFICANT PRECIPITATION WOULD
COINCIDE WITH THIS EVENT... IF IT WERE TO OCCUR AT THAT TIME.

[wxman57]

Excellent day yesterday! A record 83 degrees made for great biking weather. We rode 45 miles around the city. Was only slightly cool when the sun went behind the clouds a few times. Latest GFS doesn't indicate much in the way of a front Tuesday any more, and nice warm weather next weekend too.

[txsnowmaker]

Glad for all of those who enjoy 80s in December, but I am in the camp that is praying for wetter and cooler weather. We are entering severe drought status again, and I shudder to think about the devastation that could be in the offing if we have a repeat of 2011 dryness and heat again. As you can tell from my forum ID name, I am a fan of cold weather, but the threat of foundations cracking, wildfires threatening our communities, trees decaying and dying off in our neighborhoods and landmark areas like Memorial Park, and low lake/river water levels that harm our region's jobs and economy are a few of the reasons why I am hoping that unseasonably warm and dry weather does not continue to parch our already dry grounds and set us up for a terrible situation come next summer.

[Portastorm]

Excellent day yesterday! A record 83 degrees made for great biking weather. We rode 45 miles around the city. Was only slightly cool when the sun went behind the clouds a few times. Latest GFS doesn't indicate much in the way of a front Tuesday any more, and nice warm weather next weekend too.

Ssshhh ... nobody tell Wxman57 about the 12z GFS run and how it's very different from the 0z run. We wouldn't want him to see the cold Polar air plunging south into Texas early next (Dec. 11-12) week.

[Big O]

Excellent day yesterday! A record 83 degrees made for great biking weather. We rode 45 miles around the city. Was only slightly cool when the sun went behind the clouds a few times. Latest GFS doesn't indicate much in the way of a front Tuesday any more, and nice warm weather next weekend too.

Ssshhh ... nobody tell Wxman57 about the 12z GFS run and how it's very different from the 0z run. We wouldn't want him to see the cold Polar air plunging south into Texas early next (Dec. 11-12) week.

Do tell. The suspense is killing me.

[srainhoutx]

From NWS Dallas this morning:

MEDIUM TO EXTENDED RANGE MODELS FINALLY INDICATE A PATTERN CHANGE
ACROSS THE HEMISPHERE WITH THE PERSISTENT UPPER LEVEL CYCLONE OVER
THE GULF OF ALASKA BECOMING DISLODGED. AS IS USUALLY THE CASE WHEN
A PATTERN CHANGE IS FORECAST IN THE EXTENDED PERIODS...MODEL
GUIDANCE IS ALL OVER THE MAP WITH RESPECT TO THE PARTICULARS IN
THE FORECAST. FOR EXAMPLE...A FRIDAY COLD FRONT WAS ADVERTISED
YESTERDAY...BUT TODAY THE CANADIAN HAS THE FRONT THROUGH THURSDAY
NIGHT...THE UKMET/GFS IS WEAKER AND STALLS IT OVER THE AREA FRIDAY
NIGHT...AND THE ECMWF HAS A STRONG FRONT THROUGH ON SATURDAY. BY
MONDAY THE GFS UNLEASHES ARCTIC AIR INTO THE PLAINS...BUT THE
ECMWF DOES NOT HAVE THIS SURGE AND HAS A MUCH DIFFERENT UPPER
PATTERN FORECAST. IT GOES WITHOUT SAYING THAT THE FORECAST BEYOND
5 DAYS IS OF VERY LOW CONFIDENCE...AND THERE IS LITTLE CHOICE BUT
TO TREND TEMPERATURES TOWARD CLIMO FRIDAY...SATURDAY AND SUNDAY.
SO WHILE THE TEMP FORECAST SHOWS COOLING...THIS IS REALLY AN
ARTIFACT CAUSED BY TRYING TO FORECAST WITHOUT A RELIABLE SIGNAL IN
THE MODELS. WILL ENTERTAIN THE IDEA THAT A WEAK FRONT MAY AFFECT
THE AREA FRIDAY NIGHT AND/OR SATURDAY AND KEEP 20 POPS IN
FORECAST. AGAIN THIS IS OF LOW CONFIDENCE...AND IF POPS WERE NOT
ALREADY IN THE FORECAST FROM YESTERDAY THEY WOULD HAVE PROBABLY
BEEN LEFT OUT.




And from the HPC:

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
901 AM EST SUN DEC 02 2012

VALID 12Z THU DEC 06 2012 - 12Z SUN DEC 09 2012

...SYNOPSIS...

THE WESTERN U.S. STORM RELAXES DURING THE MEDIUM RANGE PERIOD. IN
THE EASTERN U.S...A SLOW MOVING FRONT WILL BRING A CHANCE OF RAIN
AND POSSIBLY A ZONE OF WINTRY MIX BY NEXT WEEKEND.

THE MEDIUM RANGE FORECAST FEATURES A GRADUAL CHANGE IN THE LARGE
SCALE PATTERN. A LONG-LIVED REX BLOCK AND SPLIT FLOW REGIME
NEAR/SOUTH OF THE ALEUTIAN ISLANDS WILL BREAK DOWN. THIS ALLOWS
MORE COLD AIR TO SPILL OFF OF CONTINENTAL ASIA AND DEEPEN A
LONGWAVE TROUGH OVER THE CENTRAL PACIFIC. THIS PROPS UP A RIDGE
OVER THE EASTERN PACIFIC...BRINGING AN END TO THE PROLONGED HEAVY
RAIN EVENT ALONG THE WEST COAST OF THE U.S. DOWNSTREAM...MODELS
AND TELECONNECTIONS PREDICT DEVELOPMENT OF A BROAD SCALE
POSITIVELY TILTED TROUGH...SUPPORTED BY INTRUSIONS OF ARCTIC AND
MODIFIED ARCTIC ARE INTO THE CENTRAL/EASTERN STATES.

...MODEL CHOICE...

GUIDANCE CONTINUES TO SHOW THAT UNCERTAINTY IN SOME DETAILS OF
NORTHERN PACIFIC FLOW BY THE MIDDLE OF THE WEEK WILL LEAD TO
GREATER THAN DESIRED SPREAD FOR SHORTWAVE SYSTEMS PROGRESSING
DOWNSTREAM WITHIN THE DEVELOPING LONGWAVE TROUGH OVER NORTH
AMERICA. SUCH A PATTERN WOULD LEAD TO A FRONTAL BOUNDARY EXTENDING
FROM THE SOUTHERN PLAINS TO NEW ENGLAND BY DAYS 6/7...WITH
POTENTIAL FOR ONE OR MORE WAVES TO EVOLVE ALONG THE FRONT. SPREAD
AMONG LATEST AND RECENT OPERATIONAL MODELS/INDIVIDUAL ENSEMBLES
CONTINUES TO BE SUFFICIENTLY LARGE LATE IN THE PERIOD TO FAVOR
RELYING ON ENSEMBLE MEANS TO CAPTURE THE MORE PREDICTABLE LARGE
SCALE PATTERN...WHILE WAITING FOR BETTER AGREEMENT AS TO THE
DETAILS.

ALTHOUGH THE GFS HAS SOME QUESTION MARKS WITH ITS CNTRL-ERN CONUS
EVOLUTION IN THE SHORT RANGE... BY EARLY DAY 3 WED A BLEND OF THE
00Z GFS/ECMWF APPEARS REASONABLE FOR THE SYSTEMS REACHING W-CNTRL
NOAM AND THE EAST COAST AT THAT TIME. THIS BLEND IS CONTINUED
THRU DAY 4 THU. A SLIGHTLY GREATER WEIGHTING OF THE GEFS/12Z
ECMWF ENSEMBLE MEANS IS INTRODUCED DAY 5 FRI AS FCST SPREAD OVER
THE PACIFIC COMES INTO THE PICTURE. A BLEND OF THE 12Z ECMWF/00Z
GEFS MEANS SERVES AS THE STARTING POINT FOR DAYS 6-7 SAT-SUN WITH
THE GOAL OF YIELDING SOMEWHAT BETTER CONTINUITY THAN WOULD LIKELY
BE THE CASE IF SELECTING PARTICULAR DETAILS OF ANY CURRENT
OPERATIONAL SOLUTIONS.

...IMPACTS...

THE TAIL END OF THE WESTERN U.S. RAIN/SNOW STORM WILL BE WINDING
DOWN BY DAY 3 AS HEIGHT FALLS MIGRATE FARTHER INLAND AND THE UPPER
FLOW FLATTENS. ON DAYS 4/5 THE PACIFIC ENERGY COMES INTO PHASE
WITH CONTINENTAL AIR DIPPING SOUTHWARD TO CARVE OUT A VERY BROAD
TROUGH OVER THE NATION. TEMPERATURES WILL REMAIN NEAR OR ABOVE
AVERAGE FOR DECEMBER IN THE SOUTHERN TIER AND UP ALONG THE EAST
COAST...AHEAD OF THE ASSOCIATED FRONTAL BOUNDARY. BACK TO THE
NORTH AND WEST OF THE FRONT...TEMPERATURES WILL DROP TO NEAR OR
JUST SLIGHTLY BELOW AVERAGE. PRECIPITATION IS LIKELY TO BREAK OUT
AND BECOME ORGANIZED WITHIN THE PRIMARY FRONTAL ZONE BY DAYS
5-7...ESPECIALLY FROM THE MID/LOWER MISSISSIPPI VALLEY TOWARD
SOUTHERN NEW ENGLAND. SOME WINTRY MIX OF RAIN/ICE/SNOW COULD OCCUR
AT THE NORTHERN FRINGE OF THIS PRECIPITATION.

RAUSCH/BURKE



00Z European Ensembles:

12Z GFS Operational:

[SusieinLP]

I am not a fan of arctic weather, but I am currently decorating my Christmas Tree with the AC running.... I'd be happy with highs in the low 60s. However...I would trade some cool temps for a couple of inches of rain. I've been reading about pattern changes since the beginning of November. Hopefully we get a break soon

[Ptarmigan]

Glad for all of those who enjoy 80s in December, but I am in the camp that is praying for wetter and cooler weather. We are entering severe drought status again, and I shudder to think about the devastation that could be in the offing if we have a repeat of 2011 dryness and heat again. As you can tell from my forum ID name, I am a fan of cold weather, but the threat of foundations cracking, wildfires threatening our communities, trees decaying and dying off in our neighborhoods and landmark areas like Memorial Park, and low lake/river water levels that harm our region's jobs and economy are a few of the reasons why I am hoping that unseasonably warm and dry weather does not continue to parch our already dry grounds and set us up for a terrible situation come next summer.

I want wetter and cooler or just wetter. Drought threat is real and it is bad. I have noticed when there is a widespread drought, it preceeds or occurs during a recession. The 1930s drought contributed to the Great Depression. The 1950s had a recession in 1953 and 1957-1958 as Texas came out of the drought. The drought had damaged Texas's agriculture industry. A large portion America was in a drought in 1977 during a period of stagflation.

Percentage America In Moderate To Extreme Drought
http://www1.ncdc.noaa.gov/pub/data/cmb/ ... ry-mod.txt

State Of The Climate Drought
http://www.ncdc.noaa.gov/sotc/drought/

[srainhoutx]

Haha, I'm not saying it won;t happen. Just being extra cautious after jumping on the band-wagon when these indications first started appearing in the longer ranges around mid-November. I'm just going this comes to fruition before the 19th or so. I come home to Houston on the 19th; obviously my chances of winter precipitation are much greater up 'in these parts'.

lol...

[weatherguy425]

Haha, I'm not saying it won;t happen. Just being extra cautious after jumping on the band-wagon when these indications first started appearing in the longer ranges around mid-November. I'm just going this comes to fruition before the 19th or so. I come home to Houston on the 19th; obviously my chances of winter precipitation are much greater up 'in these parts'.

lol...

I was definitely getting worried when models kept pushing this amplification and pattern change further and further back. THANKFULLY models are just starting to agree on when the initial cold push may impact Texas (10-12th). May even have more than one winter weather event before I head to Houston for a week! Though, moisture quality this far northwest is always troublesome, but with a system like that it may not be all that hard.

[srainhoutx]

Some scattered showers are moving N to NE from offshore of Matagorda Bay to Lake Charles. Coastal Counties may see a brief shower as moisture increases across the region. Fog may be an issue for the morning commute as well.

[srainhoutx]

The 00Z NAM (WRF/NMM) meso models are suggesting E TX/W Louisiana may have increasing storm chances late Monday into Tuesday as a weak Pacific front sags SE and a short wave moves through the region. The SPC has mentioned this region for potential storm chances as well.

[srainhoutx]

Those showers that were offshore overnight have moved inland and the SPC has SE TX outlined today for a chance of non severe storms. Tomorrow the chances increase as an upper air disturbance heads E across the Lone Star State and a weak cool front approaches the area. The SPC again outlines areas from the Valley/Central TX on E where some stronger storms are possible mainly near the Sabine River and Western Louisiana.

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0657 AM CST MON DEC 03 2012

VALID 031300Z - 041200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
EARLY-MORNING WATER VAPOR LOOPS DEPICT A SHORTWAVE TROUGH
PROGRESSING EWD OVER THE CNTRL UNITED STATES...NOW EMERGING OVER THE
HIGH PLAINS. THIS FEATURE WILL CONTINUE TO TRACK EWD THROUGH THE
REMAINDER OF THE PERIOD...WHILE AN ACCOMPANYING SFC LOW MOVES
EWD/ENEWD FROM SERN MANITOBA TO JAMES BAY. A STRONG COLD FRONT
TRAILING SOUTH OF THE LOW WILL SURGE EWD ACROSS THE UPPER/MIDDLE MS
VALLEY TO THE GREAT LAKES REGION...WHILE THE SRN EXTENT OF THE SAME
FRONT SHIFTS SEWD/SWD ACROSS THE CNTRL/SRN PLAINS. BY EARLY TUE
MORNING...THE FRONT WILL EXTEND FROM THE WEST END OF LAKE ERIE TO
CNTRL AR TO SWRN TX. THE FRONT WILL SERVE AS THE FOCUS FOR
THUNDERSTORMS...A FEW POSSIBLY SEVERE...FROM THE GREAT LAKES TO AS
FAR SOUTH AS NERN TX LATE THIS AFTERNOON INTO TONIGHT. A SEPARATE
AREA OF ISOLATED NON-SEVERE STORMS MAY EVOLVE ACROSS SERN TX AND
SWRN LA INVOF A LOW-LEVEL CONFLUENCE AXIS AND RELATIVELY RICHER
MOISTURE.

The attachment 12032012 SPC day1otlk_1300.gif is no longer available

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1254 AM CST MON DEC 03 2012

VALID 041200Z - 051200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
AN EVOLVING UPPER TROUGH OVER THE CENTRAL U.S. EARLY WILL CONTINUE
ITS EWD PROGRESSION...EXPANDING TO COVER ALL OF ERN NOAM BY LATE IN
THE PERIOD. AS THIS TROUGH SHIFTS EWD...A MORE
ZONAL/LOWER-AMPLITUDE WLY FLOW FIELD WILL EXPAND OVER THE
WEST...THOUGH A TREND TOWARD WEAKLY CYCLONIC CURVATURE WILL OCCUR AS
A SHORT-WAVE TROUGH APPROACHES THE WRN CANADA COAST.

AT THE SURFACE...A COLD FRONT STRETCHING FROM THE ERN UPPER GREAT
LAKES REGION SWWD INTO NERN TX WILL ALSO MAKE EWD PROGRESS WITH TIME
-- PARTICULARLY ACROSS THE NORTHEAST. BY THE END OF THE
PERIOD...THE FRONT SHOULD APPROACH THE NEW ENGLAND/MID-ATLANTIC
COASTAL AREAS. FARTHER SW...THE FRONT IS EXPECTED TO DRIFT MORE
SLOWLY SEWD...LINGERING INVOF THE UPPER TX/CENTRAL GULF COASTS
THROUGH LATTER STAGES OF THE PERIOD.

AS LOW-LEVEL MOISTURE STREAMS NWD AHEAD OF THE FRONT...VERY WEAK
DESTABILIZATION IS EXPECTED...WHICH WILL SUPPORT SHOWERS AND
OCCASIONAL LIGHTNING -- POSSIBLY AS FAR NEWD AS THE MID/UPPER OH
VALLEY. MOST SUBSTANTIAL/WIDESPREAD LIGHTNING IS EXPECTED TO OCCUR
INVOF THE LOWER MS AND SABINE RIVER VALLEYS...WHERE GREATER
LOW-LEVEL MOISTURE SHOULD SUPPORT SLIGHTLY MORE SUBSTANTIAL CAPE.
HAVING SAID THAT...SEVERE POTENTIAL APPEARS TO REMAIN QUITE LOW. AS
HAS BEEN THE CASE THE PAST SEVERAL FORECASTS...MODELS CONTINUE TO
DEPICT FLOW THROUGH THE MIDDLE TROPOSPHERE LIKELY TO REMAIN AOB 30
KT ACROSS THIS REGION...WHICH -- COMBINED WITH ONLY MARGINAL
INSTABILITY -- SUGGESTS DISORGANIZED/SUB-SEVERE STORMS. WHILE
LOCALLY GUSTY WINDS AND SMALL HAIL MAY OCCUR IN A FEW AREAS...SEVERE
POTENTIAL APPEARS TO REMAIN BELOW 5%.

Now for the pattern change we have been advertising. The guidance has come into somewhat better agreement suggesting a strong front will drop S from Western Canada during the week into the Intermountain West/Plains. The Euro suggests the front will arrive Sunday while the GFS is about 12 – 18 hours slower suggesting a Monday frontal passage. The bigger news is the wintry mischief that may be associated with that stronger front across the Panhandle and N Texas/Oklahoma. The Euro is a bit more progressive and leaves a 500mb low near the California/Baja Coast while the GFS moves that Upper Low across the Panhandle next week and drops a much stronger Arctic front S near the 10, +/- a day or two. All in all the warm weather of this week appear to be a distant memory next week as some of that very cold air that has been building across Western Canada drops S into the Lower 48. Temps in the Yukon Territory (near Dawson) have been dropping near -40 C for lows with highs in the –teens to lower -20’s for highs. All that said I do believe a much stormier pattern is a short week away with wintry mischief threats across the Rockies/Plains and even as far S as Texas. We will see.

NWS Dallas/Ft Worth:

HOWEVER...BIG CHANGES ARE ON THE WAY AS THE LARGE UPPER LEVEL
CYCLONE THAT HAS MADE ITS HOME OVER THE GULF OF ALASKA FOR THE
LAST 2 WEEKS GETS KICKED EASTWARD AND ONSHORE BY THE WEEKEND. AS
THE TROUGH HEADS EAST ACROSS THE CONUS...IT WILL UNLEASH ARCTIC
AIR THAT HAS BEEN BOTTLED UP OVER WESTERN CANADA FOR MOST OF
NOVEMBER. THIS UPPER PATTERN IS NOT ANYTHING SPECIAL OR UNIQUE FOR
COLD AIR INTRUSIONS...SO RECORD COLD IS OUT OF THE QUESTION.
HOWEVER THE AIR THE TROUGH TAPS INTO IS FAIRLY COLD AND WILL
CAUSE A QUICK ARRIVAL OF WINTER TYPE WEATHER EARLY NEXT WEEK. THE
00Z GFS DIGS THE UPPER LEVEL ENERGY INTO THE INTER-MOUNTAIN WEST
WHICH HOLDS UP THE FRONT ABOUT A DAY BUT WOULD INCREASE THE CHANCE
OF FROZEN PRECIP. AS OF NOW THE 00Z GFS IS THE OUTLIER...AND THE
ECMWF OFFERS A GOOD COMPROMISE OF 500MB PATTERNS SHOWN BY THE
UKMET...CANADIAN...AND GFS ENSEMBLE MEAN. SO ALL OF THIS POINTS
TO THE COLD FRONT ARRIVING MONDAY...12-24 HOURS FASTER THAN THE
CURRENT 00Z GFS. WINTER PRECIP CANT BE RULED OUT...BUT RIGHT NOW
IT IS A VERY LOW PROBABILITY EVENT. EITHER WAY...TEMPS WILL FALL
DURING THE DAY MONDAY WITH LOWS IN THE 20S BY TUESDAY
MORNING...AND HIGHS TUESDAY LIKELY STUCK IN THE 30S OR 40S.

[srainhoutx]

The 12Z GFS certainly raises an eyebrow for the Southern Rockies/Southern Plains suggesting a Winter Storm across New Mexico/Colorado/The Panhandles of Texas and Oklahoma early next week...

500mb Vort:

The attachment 12032012 12Z GFS 12zgfs500mbvort162.gif is no longer available

850mb surface chart:

[wxman57]

Latest GFS indicates the current very nice weather will continue through next Monday, though we'll have to put up with a few cool days Wed/Thu of this week. But quite a precarious temperature drop predicted for next Monday night. Of course, the same model a week ago had low temps here the 30s for tomorrow, so maybe there's hope it won't be so cold next Tue/Wed.

Note - the 12Z Euro has quite a different flow pattern than the GFS for later this week through next Wednesday. It has a weak cold front moving through SE TX on Sunday while the GFS has nothing moving through Sunday. Then the GFS moves the big upper low across Texas next Tue while the Euro has it stationary well west of TX, indicating not much cold air here.

[srainhoutx]

EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
223 PM EST MON DEC 03 2012

VALID 12Z THU DEC 06 2012 - 12Z MON DEC 10 2012

GENERAL FLOW PATTERN
==============================
RELATIVELY FLAT FLOW ACROSS THE CONUS AT THE BEGINNING OF THE
FORECAST PERIOD WILL BEGIN TO AMPLIFY AS RIDGING BUILDS IN OVER
THE EASTERN PACIFIC AND BROAD UPPER TROUGHING DIGS THROUGH THE
WESTERN U.S. THIS WEEKEND. THE UPPER TROUGH SHOULD WORK ITS WAY
INTO THE CENTRAL U.S. ON MONDAY...AND A STRONG COLD FRONT WILL
BEGIN TO PUSH EASTWARD THROUGH THE PLAINS/MISSISSIPPI VALLEY.
ENSEMBLE MEANS APPEAR TO HAVE A GOOD HANDLE ON THE EVOLUTION OF
THE LARGE SCALE FLOW DURING THE MEDIUM RANGE PERIOD...BUT A DECENT
AMOUNT OF SPREAD AMONG INDIVIDUAL ENSEMBLE MEMBERS AS WELL AS
DETERMINISTIC GUIDANCE INDICATES THAT THERE IS STILL SOME
UNCERTAINTY IN THE FORECAST...ESPECIALLY BY DAY 6 AND 7. THESE
DIFFERENCES IN THE MODELS LEAD TO FAIRLY SIGNIFICANT DIFFERENCES
IN THE SENSIBLE WEATHER ACROSS THE STATES.


MODEL DIFFERENCES
==============================
THE MOST NOTABLE DIFFERENCE WITH MEDIUM RANGE GUIDANCE IS WITH
JUST HOW FAST OR SLOW THE UPPER TROUGH DIGGING THROUGH THE WEST
THIS WEEKEND WILL PROGRESS INTO THE CENTRAL U.S. ON MONDAY...AND
THEN HOW FAST A COLD FRONT WILL EJECT EASTWARD OUT OF THE ROCKIES
AND ACROSS THE PLAINS/MISSISSIPPI VALLEY. EACH PIECE OF GUIDANCE
HAS BEEN STRUGGLING WITH ITS OWN RUN TO RUN CONTINUITY ISSUES LATE
IN THE FORECAST PERIOD. RECENT RUNS OF THE GFS HAVE BEEN
ADVERTISING ONE OF THE SLOWEST SOLUTIONS...HOLDING A BULK OF THE
ENERGY BACK OVER THE SOUTHWESTERN U.S. THROUGH MONDAY MORNING. ON
THE FLIP SIDE...THE PAST FEW RUNS OF THE ECMWF HAVE BEEN MUCH
FASTER WITH PROGRESSING THE ENERGY EASTWARD INTO THE CENTRAL
U.S....AND WITH PUSHING THE ASSOCIATED COLD FRONT EASTWARD. BY
MONDAY MORNING...THE 12Z GFS AND 12Z ECMWF ARE OVER 400 MILES
APART WITH THE LOCATION OF THE COLD FRONT THROUGH THE SOUTHERN
U.S.. THE GFS KEEPS THE FRONT BACK IN THE MIDDLE MISSISSIPPI
VALLEY/SOUTHERN PLAINS...WHILE THE ECMWF RACES THE BOUNDARY OUT TO
THE SOUTHERN APPALACHIANS AND FLORIDA PANHANDLE. ALSO...THE 00Z
ECMWF IS ONE OF THE QUICKEST TO SPIN UP A SURFACE LOW...TRACKING A
PRETTY DEEP CYCLONE OVER THE UPPER GREAT LAKES BY MONDAY MORNING.
FORTUNATELY...THE ENSEMBLE MEANS ARE IN SOMEWHAT OF AGREEMENT
WITH THE TIMING ALOFT...WITH THE 00Z GEFS MEAN BEING ONLY SLIGHTLY
SLOWER THAN THE 00Z ECMWF ENSEMBLE MEAN. HOWEVER...EVEN THE MEANS
STILL SHOW SOME UNCERTAINTY WITH THE EXACT TIMING OF THE COLD
FRONT.


PREFERENCES
==============================
THE MEDIUM RANGE FORECAST STARTED WITH A BLEND OF THE 00Z
GFS/ECMWF SINCE THERE WAS DECENT AGREEMENT AMONG DETERMINISTIC
GUIDANCE. AFTER DAY 4...AN INCREASING AMOUNT OF SPREAD WITH
ENSEMBLE MEMBERS...ESPECIALLY WITH THE UPPER TROUGH PROGRESSING
INTO THE CENTRAL U.S. ON MONDAY...LED TO A TRANSITION TOWARDS THE
00Z GEFS/ECMWF ENSEMBLE MEANS. THE MORNING BLENDS RESULTED IN
MINIMAL CHANGES TO CONTINUITY...AND NO CHANGES WERE MADE FOR THE
FINAL ISSUANCE SINCE THE AVAILABLE 12Z GUIDANCE DID NOT OFFER ANY
BOOST IN CONFIDENCE FOR A PARTICULAR SOLUTION.


SENSIBLE WEATHER
==============================
CONDITIONS WILL GRADUALLY COOL OVER THE NORTHWESTERN U.S. AS THE
UPPER TROUGH DIGS IN OVER THE REGION THIS UPCOMING WEEKEND. ONCE
THE ASSOCIATED COLD FRONT EJECTS OUT OF THE ROCKIES ON
MONDAY...TEMPERATURES SHOULD DROP PRETTY QUICKLY BEHIND THE
BOUNDARY AS IT PUSHES THROUGH THE PLAINS/MISSISSIPPI VALLEY. IN
TERMS OF PRECIPITATION ACROSS THE NATION...A FRONTAL BOUNDARY
SETTING UP THROUGH THE OHIO/MIDDLE MISSISSIPPI VALLEY WILL LIKELY
BE THE FOCUS FOR A WELL ORGANIZED BAND OF MODERATE RAINS THIS
WEEKEND.


GERHARDT