Area Forecast Discussion
Issued by NWS Amarillo, TX

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721
FXUS64 KAMA 150425 AAB
AFDAMA

Area Forecast Discussion...UPDATED
National Weather Service Amarillo TX
1025 PM CST Sat Jan 14 2017

.AVIATION...
IFR conditions should prevail through this forecast. FZRA will be
common at AMA and GUY. DHT should stay just above freezing, so RA
will be common there. TSRA will continue at AMA off and on through at
least the early morning hours. FZRA may switch over to RA at AMA
Sunday afternoon, meanwhile, GUY should stay in the FZRA. The
precipitation should then start to change over to SN Sunday evening
from west to east. Winds will remain light through the morning Sunday
and then they will pick up to around 15 knots in the afternoon or
early evening.

&&

.PREV DISCUSSION... /Issued 548 PM CST Sat Jan 14 2017/

AVIATION...
IFR conditions will prevail through this forecast. Temperatures will
hover around 32 degrees for much of this forecast. Therefore,
freezing rain will be the main precip type. The freezing rain may
change over to rain Sunday afternoon in the south.  Precipitation
will not be continuous through this forecast, but visibilities will
likely drop to around 1/2 of a mile in fog in between the bouts of
precipitation.

PREV DISCUSSION... /Issued 528 PM CST Sat Jan 14 2017/

DISCUSSION...

Approaching major storm system across baja is providing over-
running sw flow above extremely shallow but cold airmass at the sfc.
Temps are still below freezing fall all but far w and sw zones this
aftn. Extreme moisture with isentropic upglide and upr diffluence in
advance of the mid-upr low are producing widespread rain and freezing
rain across the area. There are some embedded elevated thunderstorms
in unstable air above an insane warm nose where temps are near 10 deg
c. As expected the rain is not supercooled given the shallow layer of
freezing temps and therefore we are not seeing a textbook...freeze on
contact...type freezing rain event. Luckily this will continue to be
a mitigating factor that allows only a small percentage of the total
rainfall to freeze mainly on elevated surfaces which is why we
continue to limit ice accumulations to 1/2" in the warning area. Not
sure even the warning area will see these ice totals...but will let
advisories ride as is for now as darkness may allow a bit more
efficient freezing process overnight. Lows tonight will not drop much
below current readings.

When all said and done...the main story from all this may be the
amount of rain we will see through sunday. Isentropic upglide is
impressive to say the least as srly flow just above the shallow cold
airmass increases through sunday as the upper low approaches.
Strongly diffluent flow aloft and strong q-vector convergence will
aid in massive large scale lift on sunday as storm moves towards the
area. Pops are pretty much in categorical range for most of the area
and flat out showed 100% for cen zones on sunday. Elevated tstms will
provide heavy rainfall and small hail as everything coming to a head
on sunday afternoon. Storm total rainfall amounts 2" are expected and
some localized flooding is possible on sunday. The warm nose is
slowly trying to erode the near sfc cold wedge...but hard to say
exactly how far into sunday we will remain below freezing but 18z
still seems like good end time for current winter products. Like
cooler raw blends best for temps sunday which means most areas should
rise above freezing but remain below 40.

Model trends on the track of the low take it directly across the
central or se panhandle now sunday night. GFS is the only model not
showing 0 to -3 deg c h85 temps wrapping around nw side and into the
region quickly after 00z monday and is therefore the only model not
suggesting a change over to sleet and snow for at least the nw half
of the panhandle sunday night. We are leaning toward a
GEM...ECMWF...NAM12 compromise and are showing 1-4" of snow across
the NW Panhandles sunday night. There is some concern for higher
amounts as we will be in the sweet spot of the low which could lead
to some heavy snow at times unless the GFS verifies the warmer h85
temp profiles. TTU WRF also shows significant snow bands in the
region by midnight and we will have to continue to monitor for
possibility of higher snow amounts in the area. We are showing
highest snow totals in the far nw...but this portion of the forecast
is the most dependent on exact storm track...so stay tuned. Temps
show warm to near 40 north and low 50s se so snow will begin melting
quickly monday aftn.

After this weekend (target of opportunity) didn`t deviate much from
superblend. There is some uncertainty wrt another s/wv dropping
across the plains on tue but kept things dry for now with temps
rising above normal. Things could get interesting next weekend again
as models show a closed low moving very near the panhandles again. Latest
ecmwf and gfs take this system just north but there are GFS ensembles
showing a further south track. If srn track pans out could see next
rain then snow chc with this system Sat/Sun. Kept POPS at 20 for now
given uncertainty.

&&

.AMA Watches/Warnings/Advisories...
TX...Ice Storm Warning until noon CST Sunday for the following zones:
     Hemphill...Lipscomb...Ochiltree...Roberts...Wheeler.

     Freezing Rain Advisory until noon CST Sunday for the following
     zones: Armstrong...Carson...Collingsworth...Dallam...
     Donley...Gray...Hansford...Hartley...Hutchinson...Moore...
     Oldham...Potter...Randall...Sherman.

OK...Ice Storm Warning until noon CST Sunday for the following zones:
     Beaver...Texas.

     Freezing Rain Advisory until noon CST Sunday for the following
     zones: Cimarron.


&&

$$

15/11



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