Area Forecast Discussion
Issued by NWS Amarillo, TX

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FXUS64 KAMA 170359 AAA
AFDAMA

Area Forecast Discussion...UPDATED
National Weather Service Amarillo TX
959 PM CST Sat Dec 16 2017

.UPDATE...

Strong disturbance moving across the area finally found enough
moisture to spark intense enough shra which led to -RA reported
at Canadian. Not sure if we will see much more than sprinkles as
the high based precip has quite a bid of dry air to push through
to make it to the SFC, but went ahead and added a 20 pop to the
far east to account for this activity. Expect a band of low clouds
forced by strong CAA and low level lift behind the front across
the north late tonight and Sun morning. There was even some brief
indication of light drizzle noted on a few model bufkit
soundings. The drizzle might be a bit overdone, but will be
something to watch for in the morning. Otherwise, didn`t make much
changes to forecast for rest of the night.

&&

.AVIATION...

Not much change to previous forecasts with period of IFR in GUY
behind a cold front in the morning and otherwise VFR conditions.
Moderate north winds will develop behind the front between
midnight and sunrise. Winds will weaken rapidly toward sunset.

&&

.PREV DISCUSSION... /Issued 627 PM CST Sat Dec 16 2017/

AVIATION...

A cold front will move through the region through the night.
Strong cold advection will lead to low clouds and possibly even
some drizzle (or freezing drizzle) behind the front mainly in the
nrn/NE Panhandles. After looking at high res models and latest
MOS guidance, decided to show IFR conditions in the morning for
GUY but not other sites. These clouds will lift through the
morning and eventually give way back to VFR conditions area wide
in the aftn.

PREV DISCUSSION... /Issued 224 PM CST Sat Dec 16 2017/

DISCUSSION...Upper level low over southeastern New Mexico this
afternoon is lifting northeast across west Texas bringing with it
high clouds across the eastern Texas Panhandle. At the surface,
lee side cyclogenesis is occurring with noticeable pressure falls
in northeast New Mexico. Associated pressure falls along with lee
side troughing has increased pressure gradients across the area,
bringing with it downsloping southwesterly winds. Fire weather
concerns exists, which are detailed in the fire weather section
below. As the surface low continues to strengthen, it will join
with an approaching cold front and help push it across the
Panhandles late this evening. Winds in association with this cold
front will be northwesterly around 10 to 20 MPH, with high
temperatures being near to slightly cooler tomorrow.

The long awaited pattern shift has started to show signs of
occurring as a longwave trough is currently moving across the
Great Basin of the western United States, which is causing the
prevalent ridge to break down and push west. Model guidance has
indicated that a vort max will pinch off the bottom of this
trough, and become a closed low over the desert southwest. Details
have come into better focus that as this system moves south
across the region Tuesday afternoon and early Wednesday morning,
moisture will remain to the south and east of the area. A brief
reprieve will follow with a shortwave ridge passing over, with
another system potentially moving across the region late Thursday
into Friday. Model guidance difference is sufficient enough to
preclude precip chances, as the ECMWF sends the system through the
area as an open wave while the GFS cuts it off over Arizona.

It is as a result of the above mentioned model difference that
will play a major role in how the forecast evolves for the weekend
before Christmas. Both the ECMWF and GFS show an arctic frontal
boundary moving across the combined Panhandles. The uncertainty
remains whether the GFS is correct with the cutoff upper low
Saturday and Sunday, as that could potentially present with winter
weather concerns. If the ECMWF is correct, then any winter weather
precipitation that may fall would be brief. We will continue to
monitor the evolution of the weather pattern for next weekend due
to these concerns.

Bieda

AVIATION...Previous Discussion...18Z TAFs..
VFR conditions to prevail throughout the 18Z TAF issuance.
Southerly winds have already begun to pick up into the 15 to 20kt
range and are expected to remain in this range through the
afternoon. Winds will decrease around sunset and remain light
until a cold front switches them out of the north overnight
tonight. Given the orientation of the front, KDHT will see this
wind shift first then followed by KGUY and KAMA. There is some
indication that a low stratus could develop post-front at KGUY but
confidence isn`t high enough to mention in prevailing.

14

FIRE WEATHER...Fire Danger Statement continues until 5 PM CST due
to elevated fire weather conditions. South to southwest winds of
15 to 25 MPH with gusts to 35 MPH, and relative humidity values
around 15 to 20 percent, are being observed. Winds should decrease
around sunset, with relative humidities beginning to recover.
Beyond today, no fire weather conditions of significance are being
forecasted at this time through next Friday.

Bieda

&&

.AMA Watches/Warnings/Advisories...
TX...None.
OK...None.

&&

$$

88/88



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