January-Foggy Mornings/Cool & Cloudy To The Month

[srainhoutx]

The overnight guidance continues to advertise a significant winter storm across New Mexico with a growing potential for accumulating snow across the Panhandles of Texas and Oklahoma. The SREF plumes NW of the Metroplex tend to raise an eyebrow with dewpoints borderline with several plumes indicating a brief round of heavy snow near Graham. Further south in the warm sector, the short-term meso guidance is indicating a stronger Coastal low/trough developing near Matagorda moving ENE with a heavy rainfall potential along the Upper Texas Coast on E into Southern Louisiana. The trends are slowing the progression of the positive tilted cold upper trough by about 12 to 18 hours with some wrap around moisture as colder air is pulled S in the wake of the surface low and a cold pocket aloft trailing the Coastal low. The soundings become borderline with the wrap around moisture possibly ending as some very cold rain mixed with a sleet pellet or two across portions of Central and E Texas on Friday extending from near Georgetown/Temple and possibly into the Bryan/College Station to Centerville and Lufkin areas into Louisiana near Fort Polk. It is still too far out to know with any certainty, but may be worth monitoring for any surprise wintry mischief. Surface temperatures look too warm for any major problems at this time.

[brooksgarner]

Hehehehe #WinterGeek (Do we do hashtags here?)
540 line on EURO for Friday.......... it's an outlier for all other models and it'll be too warm for more than a few graupel pellets north.

[brooksgarner]

12z EURO also shows a dip in the 540 line all the way to the coast (with precip commencing) Friday afternoon... flakes for Lufkin?? A surprise 1"-3" on grassy surfaces up there? Interesting, indeed.

[srainhoutx]

The GFS and Euro are still trying to resolve exactly how the two shortwaves merge (one moving E from California with a secondary dropping S from Canada) and just how deep or wrapped up the 5H/7H low becomes. That said the WPC has increased snow fall amounts rather significantly across Northern and NE New Mexico into the Panhandles of TX/OK. Portions of the Sangre de Cristo Range could see totals exceeding a foot with some 8 inch amounts across the Upper Rio Grande Valley floor. Also the 12Z Euro is suggesting some 1-3 inch amounts of snow could fall overnight Thursday into Friday as far S as Lufkin as the upper low trails the Coastal low with some wrap around moisture. The GFS is drier, but this is one of those situations where the guidance may not latch on what the sensible weather may be until about 12 to 18 hours out. The QPF has increased rather impressively this afternoon with the WPC Day 1-3 Outlook. Near 2 inch rainfall totals across Central Texas would be welcomed at this point. For those ready to toss winter, climatology suggest that early to mid February is 'prime time' for snowfall potential across most of Texas including SE Texas which typically ends around the 17th of February.

[brooksgarner]

Amazing... it's 87° right now down in the Valley....

[jasons2k]

This is the first time I can remember - it's been many years - since I recall seeing the NWS put out 100% POPS in advance. That's pretty amazing.

I also noticed they put "100" for the POP forecast. They used to use "+" instead. I wonder if that was a policy change or an oversight. Maybe this was the first time this forecaster ever had to do it?

[Katdaddy]

Another round of dense fog this morning across the Middle and Upper TX Coast as well as SW LA so drive safe. This will be a transition day back to clouds and rain chances by the afternoon and evening. Widespread light to moderate rain tonight through Thursday night with lesser rain chances through Friday night. Most areas may not reach 50F Friday. NTX may see rain become mixed with snow Thursday night and Friday but no Winter precip for SE TX as lows will be in the upper 30s. The weekend looks great with sunny skies and highs near 60 to the low 60s.

[unome]

WPC's Heavy Snow Discussion, Days 1-3 http://www.wpc.ncep.noaa.gov/discussion ... isc=qpfhsd

...southern rockies/southwest/southern high plains/tennessee valley/appalachians/mid atlantic...

a potentially high impact storm first affecting the southern rockies/southwest and southern plains on days 1 and 2 becomes a significant snow/ice threat for the tennessee valley/appalachians/mid atlantic beginning on day 3.

two troughs...one of the the desert southwest and the other diving southward from the northern rockies will merge on wednesday and thursday into a significant upper trough over the southwest. snow is developing this morning along the front slopes of the colorado rockies and will spread southward across southern colorado/much of central/northern and eastern new mexico/southwest kansas/the panhandles of oklahoma and texas/western oklahoma/western texas and an area along the red river alley between oklahoma and texas. the heaviest snow is expected to develop along the front slopes of the rockies from central and southern colorado across parts of the san juan and sangre de cristo ranges...where there is a high probability of at least 8 to 12 inches of snow. amounts in excess of a foot of snow is expected in portions of southern colorado/northeast new mexico and the western panhandles of texas and oklahoma.

as the trough moves eastward as a positively tilted trough on thursday into early friday...snow will linger across southeastern new mexico and western texas and begin to spread eastward along the red river valley between oklahoma and texas. there is a low to moderate probability of snowfall exceeding 4 inches across southeast new mexico and western texas. there are significant differences in the amount of snow forecast for the red river valley...with only light accumulations predicted by the gfs/ecmwf and ensembles while the latest 00z nam/21z sref members forecast much higher amounts. as a result...there is a low probability of greater than 4 inches of snow along the western red river valley...although wpc forecasters tended to ignore the nam/sref in favor of the ecmwf/gfs since the qpf amounts seemed to be better correlated to a weaker system than forecast by the nam.

on day 3/friday into early saturday...the positively tilted trough moves eastward and then begins to evolve into an increasingly neutral and then negatively trough moving along the gulf coast before starting to head northeastward along the atlantic coast. while an area of confluence over the eastern us is associated with rising pressures along the eastern us ahead of this system...allowing colder air to preceded the storm before moving up along the east coast...the confluence subsides and high pressure moves off the east coast. however...there is enough cold air that a threat of snow/sleet and freezing rain redevelops along the northern fringe of the precipitation shield on friday into early saturday from the tennessee valley into the appalachians and along portions of the mid atlantic states. by saturday morning...there is a low to moderate chance of greater than 4 inches of snow from northeast tennessee/eastern kentucky into the mountains of nw north carolina/western virginia into eastern west virginia and western maryland. the highest totals are expected to be in the 4 to 8 inch range over the elevated terrain of eastern west virginia and western virginia by saturday morning...but this is only the start of this storms track along the east coast. there is also a chance that a strip of freezing rain will develop as well from extreme northeast georgia up along the spine of the appalachians into portions of the middle atlantic states...where there is a low probability of greater than .25 inches of ice from the mountains of western north carolina into western virginia. the 00z ecmwf/gfs/00z gefs mean and the 12z ecmwf ensemble mean were used to base the first guess of the snowfall/ice forecast.

the probability of 0.25 inches of ice is less than 10 percent across the contiguous us on days 1 and 2.


closer to home, we'll get some welcome rain: http://water.weather.gov/precip/index.p ... oc=stateTX

[unome]

a 50-degree spread in forecast high temps across texas on thursday http://preview.weather.gov/graphical/?z ... its=localt

WPC's National Forecast for day 2, glad that snow is not by me !

http://www.wpc.ncep.noaa.gov/national_f ... atfcst.php

[srainhoutx]

Morning briefing from Jeff:

Strong storm system will bring impacts to SE TX over the next 48 hours.

Upper level trough over the SW US will deepen (intensify) and move eastward into the southern plains on Thursday and Friday. A weak surface cold front will cross the region this morning helping to scour out the dense sea fog, but clouds will linger over the region and highs today will be 5-10 degrees colder than yesterday in the low to mid 60’s.

Rapid changes onset this evening as combined deep Pacific moisture tap and Gulf moisture begin to overrun the surface cold dome. Coastal surface trough/low will be forced near the middle TX coast early Thursday as strong height falls overspread TX from the west. Moisture values soar through the roof overnight with values at CRP approaching the climatological maximum for middle January with PWS surging to over 1.50 inches and nearing 1.75 inches. This is nearly summer moisture being worked on by wintertime dynamics…so it is going to rain and rain a lot!

Will onset light rain and showers this evening from west to east across the area with rainfall really ramping up after midnight into early Thursday as the coastal low deepens off the middle coast swinging copious moisture inland. Instability is lacking so not expecting much if any thunder, but widespread waves of light to moderate rainfall with bands of heavy rainfall is likely from after midnight to early afternoon of Thursday.

Rainfall Amounts:
GFS model output is showing a solid 2.0 inches across much of the area and given the “excessive” moisture values that will be in place this is certainly likely. Will go with widespread 1.5-2.5 inches with isolated totals of 3.0 inches. Virtually the entire area will see a good soaking rainfall, but the area along and south of US 59 stand the best shot at heavy rainfall especially Thursday morning. Even though moisture levels will approach maximum values, the lack of sustain deep convection (limited instability) should preclude short term excessive rainfall rates.

Widespread nature of the rainfall combined with already moist soils will generate run-off from this event into area watersheds and rivers. Main threat will be minor street flooding during period of heavy rainfall.

Marine:
Coastal system (low) deepens as it crosses our coastal waters Thursday/Friday. NE winds will stiffen today and then shift to ENE and increase more on Thursday. Sustained winds of 15-25mph will be likely on Thursday and this will increase to 20-30mph Thursday night as the pressure gradient tightens. This is a favorable wind direction for coastal water level rise on the upper TX coast and expect tides to begin to increase Thursday morning and peak Thursday evening before winds shift around to the NW and offshore. Current extra-tropical storm surge guidance based on the GFS model run shows both Galveston and Sabine Pass approaching 2.0 ft of total water level rise Thursday evening with almost a foot being storm surge. These levels are below critical coastal flood elevations, but will put water well up to beaches and into low lying areas. Wave run-up especially on the backside (north) of Galveston Island and the west side of Galveston Bay may result in minor coastal overwash of bulkhead protection. Could see near gale force wind gust Thursday night and Friday morning as the low pressure system moves toward the Louisiana coastal waters. Coastal water levels will rapidly fall Friday morning with strong offshore flow.

Temperatures:
Cold air advection will remain in place throughout this event with the warm sector remain far out over the Gulf waters. Temperatures will remain steady in the 40’s on Thursday and Friday. Cold portion of the main upper trough passes nearly overhead Friday afternoon with at least one model showing critical thickness values being reached for some winter precipitation north of HWY 105. Will disregard this potential at this time due to warm surface temperatures and lack of any other support from other model guidance.

Weekend:
It will be all over and done late Friday with another very nice weekend expected as the storm system departs to the east. Skies will clear Saturday with only some high clouds spilling across the region. Temperatures will range from the 30’s for lows to the 60’s for highs.

[srainhoutx]

WPC's Heavy Snow Discussion, Days 1-3 http://www.wpc.ncep.noaa.gov/discussion ... isc=qpfhsd

...southern rockies/southwest/southern high plains/tennessee valley/appalachians/mid atlantic...

a potentially high impact storm first affecting the southern rockies/southwest and southern plains on days 1 and 2 becomes a significant snow/ice threat for the tennessee valley/appalachians/mid atlantic beginning on day 3.

two troughs...one of the the desert southwest and the other diving southward from the northern rockies will merge on wednesday and thursday into a significant upper trough over the southwest. snow is developing this morning along the front slopes of the colorado rockies and will spread southward across southern colorado/much of central/northern and eastern new mexico/southwest kansas/the panhandles of oklahoma and texas/western oklahoma/western texas and an area along the red river alley between oklahoma and texas. the heaviest snow is expected to develop along the front slopes of the rockies from central and southern colorado across parts of the san juan and sangre de cristo ranges...where there is a high probability of at least 8 to 12 inches of snow. amounts in excess of a foot of snow is expected in portions of southern colorado/northeast new mexico and the western panhandles of texas and oklahoma.

as the trough moves eastward as a positively tilted trough on thursday into early friday...snow will linger across southeastern new mexico and western texas and begin to spread eastward along the red river valley between oklahoma and texas. there is a low to moderate probability of snowfall exceeding 4 inches across southeast new mexico and western texas. there are significant differences in the amount of snow forecast for the red river valley...with only light accumulations predicted by the gfs/ecmwf and ensembles while the latest 00z nam/21z sref members forecast much higher amounts. as a result...there is a low probability of greater than 4 inches of snow along the western red river valley...although wpc forecasters tended to ignore the nam/sref in favor of the ecmwf/gfs since the qpf amounts seemed to be better correlated to a weaker system than forecast by the nam.

on day 3/friday into early saturday...the positively tilted trough moves eastward and then begins to evolve into an increasingly neutral and then negatively trough moving along the gulf coast before starting to head northeastward along the atlantic coast. while an area of confluence over the eastern us is associated with rising pressures along the eastern us ahead of this system...allowing colder air to preceded the storm before moving up along the east coast...the confluence subsides and high pressure moves off the east coast. however...there is enough cold air that a threat of snow/sleet and freezing rain redevelops along the northern fringe of the precipitation shield on friday into early saturday from the tennessee valley into the appalachians and along portions of the mid atlantic states. by saturday morning...there is a low to moderate chance of greater than 4 inches of snow from northeast tennessee/eastern kentucky into the mountains of nw north carolina/western virginia into eastern west virginia and western maryland. the highest totals are expected to be in the 4 to 8 inch range over the elevated terrain of eastern west virginia and western virginia by saturday morning...but this is only the start of this storms track along the east coast. there is also a chance that a strip of freezing rain will develop as well from extreme northeast georgia up along the spine of the appalachians into portions of the middle atlantic states...where there is a low probability of greater than .25 inches of ice from the mountains of western north carolina into western virginia. the 00z ecmwf/gfs/00z gefs mean and the 12z ecmwf ensemble mean were used to base the first guess of the snowfall/ice forecast.

the probability of 0.25 inches of ice is less than 10 percent across the contiguous us on days 1 and 2.


closer to home, we'll get some welcome rain: http://water.weather.gov/precip/index.p ... oc=stateTX

Moderate snow falling currently at Taos Ski Valley. It looks like the New Mexico and Southern Colorado Ski areas could pick up a whopping 16 inches+ from this storm which will be the biggest snow storm of the season so far.

[unome]

beautiful pic srain !

[brooksgarner]

This is the first time I can remember - it's been many years - since I recall seeing the NWS put out 100% POPS in advance. That's pretty amazing.

I also noticed they put "100" for the POP forecast. They used to use "+" instead. I wonder if that was a policy change or an oversight. Maybe this was the first time this forecaster ever had to do it?

For the first time in a while, I forecasted 100% chance for rain for tomorrow -- completely independent from the NWS (I hadn't even viewed their forecast.) ... I can't speak for their policies in deciding to pull the trigger on "100%", but typically it means that all the computer models agree and all observation suggest, we're in for a soaking for much of the day.

I went for 100% for those reasons.

[srainhoutx]

The radar is beginning to light up out West as Eastern Pacific moisture streams ENE and snow increasing across the Panhandle as well as across Northern New Mexico and Colorado as the two upper air disturbances begin the merging process.

[srainhoutx]

The 2 Day QPF continues to increase suggesting portions of Central and SE Texas into Coastal Louisiana may see rainfall totals exceeding 2 inches.

[Paul Robison]

The 2 Day QPF continues to increase suggesting portions of Central and SE Texas into Coastal Louisiana may see rainfall totals exceeding 2 inches.

01212015 19Z Day 1 and 2 QPF d12_fill.gif

Hate to ask this, srainhoutex, but, should any isolated storms be strong/severe (contrary to prediction), what part of Houston would have the best chance of this happening?

And what about those winds HGX mentioned in its latest AFD? Hm?

[jasons2k]

I also noticed they put "100" for the POP forecast. They used to use "+" instead. I wonder if that was a policy change or an oversight. Maybe this was the first time this forecaster ever had to do it?

I can't speak for their policies in deciding to pull the trigger on "100%", but typically it means that all the computer models agree and all observation suggest, we're in for a soaking for much of the day.

Sorry, to clarify I was questioning if there was a policy change in the forecast code at the bottom of the AFD, as "100" used to be indicated by a "+".

For example, today's discussion shows this:

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL) 50 50 40 50 35 / 80 100 50 40 10
HOUSTON (IAH) 54 55 41 52 35 / 60 100 60 30 10
GALVESTON (GLS) 55 59 43 50 42 / 50 100 60 30 20

In years past, I have seen this instead:

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL) 50 50 40 50 35 / 80 + 50 40 10
HOUSTON (IAH) 54 55 41 52 35 / 60 + 60 30 10
GALVESTON (GLS) 55 59 43 50 42 / 50 + 60 30 20

[jasons2k]

Also, we've had some discussion in the past in this forum of the meaning of the "chance of rain" - whether it is a percentage of the area they expect to get rain, or does it mean you have a 40% of getting rain at YOUR location, etc.

I was taught in Met class - and what Harold Taft explained is - "there is X% chance of getting measurable precipitation at any given point in the forecast grid (or county)."

It seems in recent years this has been simplified or watered down to mean the % of the area expected to get precipitation. I'm a bit of a stickler for rules and the 'dumbing down' of society, such as removing the dew point from TV broadcasts, because people supposedly don't know what it means, kinda bothers me.

Anyway, I did a google search and came across this, which seems to 'officially' support what I was taught by the old schoolers:

What does this "40 percent" mean? ...will it rain 40 percent of of the time? ...will it rain over 40 percent of the area?

The "Probability of Precipitation" (PoP) describes the chance of precipitation occurring at any point you select in the area.

How do forecasters arrive at this value?

Mathematically, PoP is defined as follows:

PoP = C x A where "C" = the confidence that precipitation will occur somewhere in the forecast area, and where "A" = the percent of the area that will receive measureable precipitation, if it occurs at all.
So... in the case of the forecast above, if the forecaster knows precipitation is sure to occur ( confidence is 100% ), he/she is expressing how much of the area will receive measurable rain. ( PoP = "C" x "A" or "1" times ".4" which equals .4 or 40%.)

But, most of the time, the forecaster is expressing a combination of degree of confidence and areal coverage. If the forecaster is only 50% sure that precipitation will occur, and expects that, if it does occur, it will produce measurable rain over about 80 percent of the area, the PoP (chance of rain) is 40%. ( PoP = .5 x .8 which equals .4 or 40%. )

In either event, the correct way to interpret the forecast is: there is a 40 percent chance that rain will occur at any given point in the area.

From here: http://www.srh.noaa.gov/ffc/?n=pop

[Ptarmigan]

Looks to be a rainy one. January can be wet, like in 1891 or 1991.

You create your own precipitation type by moving around wet bulb and air temperature. You can get snow, sleet, or just rain.

http://cimss.ssec.wisc.edu/wxfest/PcpnType/pcpn.html

[jasons2k]

Looks to be a rainy one. January can be wet, like in 1891 or 1991.

You create your own precipitation type by moving around wet bulb and air temperature. You can get snow, sleet, or just rain.

http://cimss.ssec.wisc.edu/wxfest/PcpnType/pcpn.html

It's neat, but not quite right. I did a simulation for sleet and my snow and sleet turns to rain as it approaches the surface, even when I set the ground temp to well below freezing. I think the algorithms need a little work.