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Area forecast discussion 
National Weather Service Fort Worth Texas
1008 PM CST Tuesday Mar 3 2015

Update...

Corrected Thursday to Wednesday

In reference to the winter weather event...we have looked at the
incoming 0z model guidance as well as the 21z sref and all
indications are that there is an excellent setup for Post frontal
precipitation. Strong lift ahead of the upper level low that is
currently located near Baja California will spread over the region and work
in conjunction with strong frontogenesis to produce an intense SW
to NE oriented band across North Texas Wednesday night. The
primary forecast challenge is precipitation types and amounts
which hinge on the temperatures...not only at the surface but
through the atmospheric column. The previous forecast looks good
for timing of the changeover and we see no new data that suggests
we need to bump the timing up. Although the cold air does often
get here faster than the models indicate...our timing is ahead of
the usually reliable rap/NAM forecasts.

Indications from the 0z guidance continue to point toward
convective instability being available for isolated thunderstorms
with heavy sleet Wednesday evening. The strong lift will keep
cooling the middle-upper levels during the evening hours and result
in a change over to snow from northwest to southeast...and we are
more concerned about some higher amounts of snow especially north
and west of the dfw metroplex where 1-2 inches may fall. The
primary axis of precipitation looks like it will occur roughly
from Comanche to dfw to Paris...but it is tough to say just how
much of this will be spent as rain and how much would be
accumulating sleet or snow. The 21z sref raises concerns that more
than 1 inch of sleet will occur within this band...and the 0z NAM
and hi-res WRF models also show this will be the favored location
for over a half inch of sleet. A transition to snow would occur a
little later in the evening that may drop an additional inch of
snow within this precipitation axis before it begins to end from
northwest to southeast after midnight.

Also Worth noting are the wind speeds tomorrow evening. Northwest
winds of 20-25 miles per hour with higher gusts will work to reduce
visibilities below a half mile in regions where a change over to
moderate snow occurs.

For the forecast...the main change was to bump up probability of precipitation Wednesday
evening areawide. There were no major changes to precipitation
type or the timing of the change-over. However given the good
setup...we have bumped up snow/sleet amounts along and northwest of a
line from Comanche to dfw to Paris. We are now expecting 1/4 to
1/2 inch of sleet and 1-2 inches of snow northwest of a Eastland to
Denton to Bonham line. For the line from Comanche to the metroplex
to Paris...we are up to a half inch of sleet and an inch of snow.
Amounts taper off as one heads farther south...but did bump the
zone from Waco to Athens up to a 1/4 to 1/2 inch of sleet.

We are on the cusp of upgrading a portion of the Winter Weather
Advisory to a Winter Storm Warning and if the 0z GFS had not come
in with a farther southward displacement of the main quantitative precipitation forecast axis in
comparison to the other models...we probably would have had the
confidence to upgrade now. We will deffer any decisions to the
next shift who will have the benefit of the European model (ecmwf)...European model (ecmwf)
ensemble...GFS ensemble...and 3z sref. Warning or not...this
certainly looks like it should be a high impact winter weather
event for a good portion of the County Warning Area.

Tr.92

&&




Short term...

..another bout of winter weather Wednesday afternoon through
Wednesday night...

Temperatures today did not warm as much as we thought and the
dense fog persisted somewhat longer. Still have a few locations
with visibility below one mile...but weak showers and drizzle
should help improve them a little before evening. But do not
expect temperatures to cool much overnight and will keep areas of
fog most of the night.

The cold front was just moving into the Texas Panhandle and
northern Oklahoma at 2 PM. Temperatures were in the teens and 20s
behind the front over Kansas. We expect the front to cross the
Red River just after midnight...into the I-20/30 corridor around
daybreak and through the far southeast counties 4-5 PM. It will
turn noticeably colder and windy behind the front. May need a Wind
Advisory for Wednesday night if MOS guidance numbers are right.
The freezing line will lag many hours behind the front...thus a
precipitation transitioning to a wintry mix may not take take
place in the northwest until middle afternoon and across the dfw
metroplex until 5 PM. Although this is our best guess on the
transition...an hour or two earlier would result in more serious
travel impacts for the afternoon commute. We have issued a Winter
Weather Advisory in three segments. One for the earlier northwest
timing...one for the central areas including the metroplex to
cover the late afternoon commuter impact potential and one in the
southeast where the transition occurs later Wednesday night.
Currently...we feel sleet amounts up to 1/2 inch and freezing rain
amounts up to 1/10 inch are the most logical for this event.

Nearly all of the models have come into better agreement on
timing...transition and amounts of precipitation. The hi-res
models are also indicating a potential for convective elements
moving over the Post-frontal cold air Wednesday evening. Sleet
showers would result in roads becoming covered in a shorter period
of time. Other factors aiding this event are: strong frontogenetic
forcing...significant lift associated with the right-rear entrance
region of the 250 mb jet aloft and a piece of shortwave energy
moving over the County Warning Area.

We will be watching new data as it arrives to re-evaluate the
potential of this system as a few minor deviations here and there
could cause significant changes to later forecasts.

The precipitation will shift to the southeast counties on
Thursday morning and should end before midday. Wind chills will be
in the middle teens to lower 20s daybreak Thursday. Highs on
Thursday will be in the middle to upper 30s with around 40 from
Cameron to Centerville. Expect sunshine to return to the entire
County Warning Area by Thursday afternoon!

&&

Long term...
an upper level split-pattern will be developing by late week with
a short wave trough arriving from the west on Saturday. Temperatures
will slowly moderate through the period...and there could be some
light showers over the southeast counties on Saturday. Highs will
start out in the middle 40s on Friday and warm into the 60s for
Monday and Tuesday. Lows will be in the 20s on Friday morning...in
the upper 20s and 30s on Saturday then warming into the 40s by Tuesday
morning. 75

&&



Preliminary point temps/pops...
Dallas-ft. Worth, Texas 48 48 26 39 24 / 60 100 90 10 5
Waco, Texas 50 61 30 39 24 / 40 90 90 20 5
Paris, Texas 43 50 25 39 23 / 70 100 90 10 5
Denton, Texas 48 48 24 39 23 / 70 100 90 10 5
McKinney, Texas 46 47 25 39 24 / 60 100 90 10 5
Dallas, Texas 48 48 26 40 25 / 60 100 90 10 5
Terrell, Texas 49 52 27 40 23 / 50 100 90 10 5
Corsicana, Texas 51 59 31 39 25 / 40 100 90 20 5
Temple, Texas 52 64 30 39 25 / 30 90 80 30 5
Mineral Wells, Texas 50 50 24 38 22 / 80 100 90 10 5

&&

Forward watches/warnings/advisories...
Winter Weather Advisory from 3 PM Wednesday to noon CST Thursday
for txz093>095-103>107-116>123-129>134-141>145.

Dense fog advisory until 6 am CST Wednesday for txz091>095-
102>107-117>121-131>134-143>146-156>161-174-175.

Winter Weather Advisory from midnight Wednesday night to noon
CST Thursday for txz135-146>148-156>162-174-175.

Winter Weather Advisory from noon Wednesday to noon CST Thursday
for txz091-092-100>102-115.



&&

$$

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