Wednesday Morning Update

Wednesday, November 20th 2013, 4:44 am
By: Alan Crone

Good Morning.  Our main focus will be on the big arctic front arriving late Thursday with much colder air lasting through the weekend into early next week.  There will be some rain and thunderstorm activity with this system, and there is a very slight chance for some wintry precipitation Friday across northwestern OK and Friday night across the I-40 corridor.  Any wintry precip is expected to remain very light and no adverse travel conditions are expected.   

Today will be another windy and relatively mild day with highs in the upper 50s and lower 60s.  South winds from 15 to 20 mph will be common with a few higher gusts along with mostly cloudy conditions.  Low level moisture will be streaming back across the state today and a few spotty showers may be possible.  This chance will be low and I'll carry only a 20% chance on the big 7 day planner.  We've been experiencing a few spotty showers and thunderstorms this morning across the northern third of the state.   

A short wave will travel across the inter-mountain region today and tonight.  As this system passes the central plains, a strong surge of shallow arctic air will rapidly move southward as a surface ridge of high pressure will build down through the Rockies.  This front should enter northwestern OK by Thursday midday and then across southern Kansas and Northern OK by afternoon to early evening.  Model data is typically too slow with these very cold and shallow arctic air masses.  I've seen these types of fronts arrive a good 6 hours ahead of schedule from model data in the past.  We still have a little wiggle room before we'll attempt to nail down the specific time, but my first shot would be Thursday evening around 4-6pm.  The actual data suggest about 9pm-10pm for the Tulsa metro.

 Before the real deal front arrives, scattered showers and storms will be increasing across the region, including a slight chance today.  A few showers or storms will be likely later tonight into pre-dawn Thursday across south-central OK and move NE into northern OK and southern Kansas.  These are not expected to be severe, but some convective energy aloft should provide for some thunder and some small hail.  

The rain-t-storm coverage is expected to increase Thursday as moisture streams northward.  The shallow nature of the air mass may allow the boundary to temporarily slow down as it encounters slightly higher terrain of eastern OK Thursday night.  A second and deeper surge of cold air will arrive Friday morning and shove this air mass across the entire southeastern OK area.  In the past, very shallow air masses have completely stalled through the Pushmataha to southern Leflore county areas southward.  Years ago, I remember temps in the Sherman-Denison area near 32 with ice and Bonham to Paris TX in the upper 40s and lower 50s with rain.  This air mass will be deep and strong enough to cover the entire area.   

Showers and rain will remain possible behind the boundary due to warm southwesterly flow over the shallow dome of cold air.  And the model data continues to diverge at this point.   

The NAM offers a big chunk of moisture Friday night riding up through the southern and east central portion of the state with temps slightly below freezing.  This would result in some icing issues.  GFS takes most of the precip south of the Red River by Friday afternoon and early evening.  This would result in no winter precip issues.  And now the EURO is finally coming around to more of the GFS solution.  I would feel much better about this forecast if the NAM would also follow suit.  Last night, the 18NAM kept the 32 isotherm just west of the region while most of the precip was exiting east late Friday night.  This morning the latest run has part of NE OK around 31 to 32 by late Friday afternoon.  A close call. 

Saturday morning the precip will be gone but the cold air will remain.  We have discounted some of the computer numbers and have used some observational data with past experience to come up with some weekend temps.  Regardless, it will be quite cold. 

A southwestern US cut off low will eventually move across the desert southwest early next week and weaken.  This feature has the potential to bring more rain and thunderstorm activity to Texas early next week and could bring some wintry precip to Oklahoma.  As stated yesterday, I think it's prudent to concentrate on the first system arriving Thursday and we'll worry about trying to peg the second one during the next day or two. 

The official high in Tulsa yesterday was 59 recorded at 12:47pm. 

The normal daily average high is 59 and the low is 38.

Our daily records include a high of 81 from 1989 and a low of 16 from 1937. 

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Thanks for reading the Wednesday Morning Weather Discussion and blog. 

Have a good day!

Alan Crone