Monday, January 5, 2009

Freezing Drizzle & Sleet Possible this AM in southern & central OK

The latest 0Z Adonis Microcast local model run shows patchy sleet continuing overnight southeast of OKC. A fairly large area of light freezing drizzle and sleet is progged to cross the Red River into southwest OK near Frederick around 8 am. The model holds the precip down close to the Red River for a few hours and then allows temps to rise above freezing. However, we have noticed the NAM gridded data handles temperatures much better than any MOS. The 0Z NAM grids hold the temperature at or below freezing across all of southern and central OK until 11 a.m. Combine that with what Adonis Microcast is showing, and you get a fairly expansive area of light to moderate freezing rain from Altus to north of Chickasha to near Durant. The heaviest area is progged to be south of Lawton and Duncan to near Ardmore.By 1 pm, all areas are above freezing except south of Duncan and toward Ardmore where temperatures remain near freezing, possibly due to heavy icing from the model. This will be an odd day where temperatures are coldest in the precip area with gradually warmer temperatures in the northwest part of the state where cloud ceilings will be the highest off the ground. Northwest OK may enjoy a few breaks in the clouds and reach the low 40s. The upper level system responsible for this mess will move from west Texas to northeast Texas during the day. Freezing rain advisories are up for the Dallas Fort Worth Metroplex.Our local WRF-ARW model shows a gradual wind shift from north to south, starting first across northwest OK and gradually working it's way south. I think winds may go calm near noon as the shift occurs in OKC. The south winds should help push temperatures above the freezing mark in many areas. This will be another reason NW OK is the warmest today.Meanwhile, upstream, a Denver low forms along the Palmer Divide this afternoon. The tail end of the south Texas cold front links up with a trough north of the Denver low to form a new weak front along the lee of the Rocky mountain chain. This new front, or weak trough, begins to move east and will cross Oklahoma on Tuesday, bringing a milder airmass. Winds should shift northwest with it's passage.On Wednesday, a southwest wind returns and I am going above MOS on temperatures. 63 may be too conservative for OKC. Western OK will likely be in the upper 60s I'm thinking.A backdoor cold front pushes into northeast OK early Thursday. I suspect winds may stay east or southeast in OKC right along it. Temperatures will probably be in the 50s.DGEX, ECMWF and now the 0Z GFS bring in a front on Friday, around noon in OKC. This front has some cold air behind it but not a lot. I think 40s return on Saturday. Sunday may wind up with a southwest wind and we may need to push temperatures back into the 60s again.Fronts continue to come every two to three days. A fairly significant high builds in western Canada in about 10 days but the cold air from it may very well slide mostly to our east.
12 day:OKC 20/36 28/46 28/63 35/56 36/56 24/42 26/56 33/52 33/48 33/57 34/44 28/5430% OKC today, beyond that all pops zero.
Daily cloud codes: CBBUBUUUBEUUC=cloudy, B=partly cloudy/mostly sunny, U=sunny, E=mostly cloudyBreezy Tuesday, Friday, Monday, next Thursday.
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