#5230 Postby srainhoutx » Sun Feb 22, 2015 11:23 am
Morning briefing from Jeff:
Winter Storm heading for TX.
Increasing threat for ice accumulation over portions of SE TX Monday evening-Tuesday morning.
Surface cool front currently lies along a line from Columbus to BUSH IAH to Cleveland with temperatures falling into the 50’s north of this boundary and rising into the 70’s south of the boundary. Front has shown very little movement this morning and do not expect much more southerly progress for much of today…in fact some of the high resolution guidance actually lifts the front back northward midday. Of bigger importance is the arctic front currently plowing through the panhandle. Temperatures behind this boundary are in the 10’s and this air mass is moving quickly southward and should push across SE TX and off the coast this evening with a much more significant temperature fall.
Strong cold air advection will onset this evening and continue Monday. Temperatures will fall from this evening through the day on Monday. Temperatures Monday morning in the lower 40’s will gradually fall during the day toward the mid 30’s by late afternoon as ice/sleet accumulation develops over north TX on Monday. Model guidance has trended a degree or two colder for Monday night and Tuesday morning which requires the freezing line to be shifted southward bringing more of the area under the threat for freezing drizzle. Additionally, what seemed marginal freezing temperatures yesterday (30-32) are now expected to be closer to 28-30 over our northern counties Tuesday morning and this is certainly into the critical threshold for ice accumulation on bridges and overpasses. Forecast profiles continue to support a very strong warm layer aloft over top of a shallow surface freezing layer (maybe 1000-2000 ft thick). This continues to support a rain/freezing rain P-type…however some of the latest soundings are showing a smaller warm layer aloft from Huntsville to Livingston Tuesday morning and this could support a mixture of freezing rain and sleet over Walker, Polk, Trinity, and San Jacinto Counties.
Freezing Line:
Of course the critical factor is how far south the freezing line progresses into the region. Current indications suggest the freezing line will extend from Columbus to Waller to between Conroe/The Woodlands to Cleveland from late Monday evening through Tuesday morning. This line has been shifted southward about 50 miles since yesterday. Both GFS and NAM guidance do suggest BUSH IAH does fall to 31-32 for a window Tuesday morning and this is possible between roughly 1100pm Monday and 900am Tuesday. Official forecast has IAH falling to 32 Tuesday morning so pockets of freezing temperatures are possible over northern and northwest Harris County overnight Monday into Tuesday morning. Best thinking at the moment is that the north and west portions of Harris County will fall to 32-33 with the rest of the county and metro Houston falling to 33-34. A degree or two could make all the difference between minor ice accumulation in Harris County and no ice at all.
Ice Accumulation:
Forecast models show general lift being maintained Monday night into early Tuesday when critical temperatures will be reached over portions of the area. Liquid QPF amounts range from .05-.10 of an inch in mainly a drizzle or light rain. Ice accumulation will be greatest from Huntsville to Livingston where temperatures will be colder the longest and likely fall into the upper 20’s resulting in effective freezing of the liquid precipitation. Accumulations in this area will likely average .05-.10 of an inch which is just under the .12 of an inch for our local winter storm warning criteria. North of a line from Columbus to Waller to Conroe to Cleveland ice accumulation of .03-.06 of an inch is possible. Temperatures in this area will be in the 30-32 degree range resulting in a less effective freezing process since the falling precipitation will need to be cooled after passing through the warm layer aloft. Bridges and overpasses are also fairly warm from the recent warmth and will take time to cool to freezing so this region has a more conditional ice accumulation threat especially on bridges and overpasses.
Decision Support Matrix:
Burleson, Madison, Walker, Trinity, San Jacinto, Polk:
Ice Accumulation: .05-.10 of an inch
Timing: 600pm Monday-1000am Tuesday
Temperatures: 28-30 degrees
Winds: NNE 10-15mph
Confidence: high
Transportation: prepare for anti-ice operations
Education: delays and cancellations possible
Aviation: anti-ice operations likely
Power: isolated outages possible
Brazos, Grimes, Washington, Montgomery, Waller, northern Liberty:
Ice Accumulation: .03-.06 of an inch
Timing: 1000pm Monday-1000am Tuesday
Temperatures: 30-32 degrees
Winds: NNE 10-15mph
Confidence: moderate
Transportation: standby for anti-ice operations
Education: delays and cancellations possible
Aviation: anti-ice operations likely
Power: isolated outages possible
Austin, Colorado, north Harris, central Liberty:
Ice Accumulation: patchy ice accumulation possible
Timing: 1100pm Monday-900am Tuesday
Temperatures: 31-33 degrees
Winds: NNE 10-15mph
Confidence: low to moderate
Transportation: monitor trends/standby equipment and personnel
Education: delays possible
Aviation: anti-ice operations possible at Hooks and IAH
Power: None
Fort Bend, southern Harris, Wharton, Jackson, Matagorda, Brazoria, Galveston, Chambers:
Ice Accumulation: None expected at this time
Timing: N/A
Temperatures: 33-35 degrees
Winds: NNE 14-18mph
Confidence: moderate
Transportation: None
Education: None
Aviation: None
Power: None
Will update again this evening.
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