612 FXUS64 KBRO 131725 AAB AFDBRO Area Forecast Discussion...UPDATED National Weather Service Brownsville TX 1125 AM CST Sat Feb 13 2021 .DISCUSSION...Updated for latest aviation discussion below. && .AVIATION...Less than ideal aviation conditions will be the mainstay through the TAF period. IFR conditions will continue to prevail over all aerodromes into Sunday. There could be a few pockets of MVFR, mainly at HRL and MFE today into the overnight. At BRO there could also be some periods of LIFR through the day today. Along with low ceilings, periods of rain are possible through the period. && .PREV DISCUSSION... /issued 536 AM CST Sat Feb 13 2021/ DISCUSSION...Updated for latest aviation discussion below. AVIATION...NAM forecast soundings show the saturated low level inversion remaining entrenched over the RGV due to the very cold airmass sprawling over the Gulf Coast. This will hold the ceilings down into IFR criteria for at least the short term. Some low level mixing later today may allow the ceilings edge up to MVFR levels especially for the MFE area. PREV DISCUSSION... /issued 421 AM CST Sat Feb 13 2021/ SHORT TERM (Now through Sunday): Currently, temps around Deep South TX and the RGV are hovering in the 30s to near 40 with CAA continuing across the region. A 500 mb short wave will be exiting the region later today. But this trough will be followed pretty quickly by another relatively stronger 500 mb trough which will pulling into the RGV area overnight through Sun morning. The passage of these upper level troughs will maintain good upper level divergence maintaining the pcpn threat throughout the short term. In addition, the passage of these 500 mb features will also maintain the potential for coastal surface troffing which will in turn help support the pcpn chcs. So the short term pops will be a general blend of the short term model sets. CAA will continue across the region as a large Arctic airmass remains entrenched over the central and eastern portions of the U.S. This in combination with the steady northerly surface winds across the region will hold down the temps and wind chill values throughout today. These wind chill values will likely touch close to advisory levels and will be posting a Wind Chill Advisory for all of Deep South TX except for the immediate coastal areas. The temps may rebound just a few degrees on Sun as the surface flow slackens a bit. So expect the wind chill values to remain low on Sun, but may remain just above advisory levels during the daylight hours. NAM forecast soundings show a pretty shallow subfreezing layer of colder air nudging into the northern counties later tonight through early Sun morning which may allow for some patchy areas of freezing rain or drizzle mixing in with the cold rain. Will leave this in the current forecast wording, but will not go with any advisory at this time as am uncertain whether much ice accumulation will occur through Sun morning. LONG TERM (Sunday Night through Friday): The big story in the forecast period remains the prolong period of bitterly cold temperatures through much of the period and the chance of freezing and/or frozen precipitation Sunday night into Monday morning. The secondary surge of much colder air expected for Sunday Night into Monday will cause temperatures to plunge across the region likely falling well below freezing for all but the immediate coastal regions of the RGV. The strengthening northerly surface winds will also push wind chill values dangerously low late Sunday into Monday. As the low level sub freezing layer pushes well into the region late Sunday, expect a Wintry mix of pcpn to prevail until the major 500 mb trough axis exits the region to the east Monday afternoon and evening ending the pcpn threat. So will be posting a Winter Storm Watch for most of deep south Texas as some significant icing will be a strong possibility. In addition, breezy to windy conditions will develop across the CWA Sunday night into Monday. A Wind Advisory is possible for the central and eastern portions of Deep South Texas and the Rio Grande Valley on Monday. Very cold temperatures will persist during the day on Monday with highs reaching only the mid to upper 30s. Mostly clear skies will provide strong radiational cooling Monday night into Tuesday morning. Confidence is increasing that a hard freeze will occur across all of deep south Texas, except for South Padre Island, Monday night into Tuesday morning. Additionally, wind chill values will likely be in the teens again on Tuesday morning. A brief warm trend starts Tuesday as surface winds later in the day Tuesday will finally swing around from the east to southeast allowing for a break in the CAA and some warming temps late Tuesday afternoon. Another deep diving 500 mb trough will move into the Plains States around midweek pushing another surge of colder Canadian air Wednesday Night into Thursday dropping down temperatures once again. Freezing temperatures will be possible, mainly across the northern ranchlands, Wednesday Night/Thursday morning and especially Thursday Night/Friday morning as drier air moves into the region once again and the surface winds drop off once again. MARINE (Now through Sunday): Model MSL fields indicate a pretty strong gradient in place along the lower TX throughout today and this evening as surface ridging over the eastern U.S. interacts with surface troffing over the Gulf of Mex. Later tonight into Sun, the gradient then relaxes enough to allow the Gulf winds and seas to decrease below SCA levels. However, SCEC conditions will likely linger mainly for the Gulf Waters. Will extend the SCA for the Gulf waters through 06Z Sun. Sunday Night through Wednesday Night: Hazardous marine conditions will prevail along the lower Texas coast through much of the period due to prolong period of moderate to strong northerly flow and rough seas. Gale conditions are likely on the Gulf waters Sunday night into Monday due to very strong winds and rough seas. Conditions will briefly improve Tuesday and Tuesday night as the pressure gradient weakens ahead or another cold front. Adverse conditions are expected to develop late Wednesday in the wake of the next cold front. && .PRELIMINARY POINT TEMPS/POPS... BAYVIEW/PORT ISABEL 40 37 48 31 / 40 50 60 80 BROWNSVILLE 40 36 46 30 / 40 60 50 70 HARLINGEN 38 34 44 28 / 40 50 50 80 MCALLEN 39 36 43 30 / 40 50 50 80 RIO GRANDE CITY 39 36 42 28 / 40 40 50 80 SOUTH PADRE ISLAND 47 42 53 38 / 40 60 60 80 && .BRO WATCHES/WARNINGS/ADVISORIES... TX...Winter Storm Watch from Sunday evening through Monday morning for TXZ248>255-353. Wind Chill Advisory until 6 PM CST this evening for TXZ248>255- 353. Freeze Watch from late tonight through Sunday morning for TXZ248>251. GM...Small Craft Advisory until midnight CST tonight for GMZ150-155- 170-175. && $$ This product is also available on the web at: HTTP://WEATHER.GOV/RGV 68-McGinnis/Aviation