Mesoscale Discussion 1

Issued

Dec 31, 2020, 7:38 PM CST (01:38 UTC)

Expired

Jan 1, 2021, 1:45 AM CST

In force

6 hr

Issued by

the Storm Prediction Center

Concerning

Winter mixed precipitation

The Dyess AFB radar (KDYX), 100 km from the middle of the area, began a volume at 01:39 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

994 
ACUS11 KWNS 010139
SWOMCD
SPC MCD 010138 
OKZ000-TXZ000-010745-

Mesoscale Discussion 0001
NWS Storm Prediction Center Norman OK
0738 PM CST Thu Dec 31 2020

Areas affected...Portions of western into northwest
Texas...southwestern into central Oklahoma

Concerning...Winter mixed precipitation 

Valid 010138Z - 010745Z

SUMMARY...A wintry mix is expected to continue across portions of
southwest Texas into central Oklahoma. Heavier snow will most likely
occur across portions of western Texas, while freezing rain,
occasionally mixed with sleet, is expected to be the predominant
winter weather hazard across portions of central Oklahoma over the
next several hours.

DISCUSSION...An occluding upper low across southwest TX continues to
gradually pivot northeastward, with an 850 mb low remaining nearly
stationary across portions of northern TX as of 01Z. Deep-layer
cyclonic flow supports a 925-700 mb warm conveyor belt continuing a
supply of moisture across portions of Oklahoma into northwest Texas,
but with up to 5C temperatures (mainly around 850 mb per 00Z OUN
observed sounding). The warmer temperatures in the sfc-850 mb layer
have inhibited greater winter weather precipitation rates across
portions of OK so far. However, given the southward advection of
relatively drier surface air (27-30 F dewpoints) from farther north,
temperatures may drop a few degrees over the next several hours.
Occasional instances of freezing rain have been noted from OKC to
SPS over the past couple of hours, with additional freezing rain and
sleet possible overnight as low-level temperatures continue to
gradually cool. 

Farther southwest, the 00Z MAF sounding shows a sub-freezing
troposphere, with METAR observations to the east showing
sub-freezing surface temperatures and heavier snowfall (as also
supported by KSJT dual-polarimetric radar data) over the past few
hours. An 800-1000 m deep, nearly saturated dendritic growth zone
suggests that heavier snow (perhaps a brief instance or two of 1
inch/hr rates) should continue for at least a few more hours, until
the upper-low pivots farther northward out of the area. Thereafter,
heavier snow may move into southwestern and central Oklahoma by
07-08Z per latest HRRR guidance.

..Squitieri/Bunting.. 01/01/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...TSA...FWD...OUN...SJT...LUB...MAF...

LAT...LON   31880234 32290219 32860183 33640088 34389938 35079848
            35839768 36199685 35949604 35699603 35359609 34919637
            33999730 33489772 32809822 31709889 31129907 30739966
            30840045 31070113 31880234

Mesoscale Discussions in Texas, 2021Mesoscale Discussions in Oklahoma, 2021Every mesoscale discussion in 2021

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.