Cold Sweeping Across Oklahoma

Highlights:- All POPs zero this week.
Temperatures will be in the mid 50s onMonday prior to a cold front early afternoon, cooling off during theafternoon hours. Tuesday will be cooler with highs in the low 40s andthen a brief return to mid 50s on Wednesday before the bottom fallsout that afternoon. Thursday will be quite cold with temperatures inthe low 20s. Friday will also be cold with highs in the mid 30s. Awarm-up is expected Saturday-Sunday with temperatures in the upper40s. This forecast is for Oklahoma City due to the variety oftemperatures expected this week.- Drought conditions continue for parts of the state and the rainforecast is not looking good.
Probabilities:-
Severe Thunderstorms in Oklahoma: < 5%-
Storm Chase: < 5%-
Winter Precip: < 5%
Discussion:While sensible weather as a whole will be limited this week, therewill be three cold front passages in Oklahoma that will keep lifesomewhat interesting. These cold fronts are in response to shortwavetrofs moving southeast into the mean longwave trof position over theeastern CONUS. The amplifying ridge just off the west coast providesconfidence in the overall pattern this week. The resulting northerlymidlevel flow aloft will provide a conduit for cold air as coldsurface highs are dislodged from Canada.The models have been jumping all over the place the past few days withthe forecast this week. Finally, the 18z GFS/NAM and 12z ECMWF are inagreement regarding the surface pattern evolution and resultanttemperatures. BUFKIT was quite helpful in analyzing expected timingof said cold fronts and comparison of run to run variations in themodels. This was especially problematic regarding the Tuesdayafternoon time period as I had extension discussions with Andyregarding the expected max temperatures.As noted above, I'm going all POPs zero this week. BUFKIT for the 18zGFS has 0.000 inches of rain for the entire 180 hour period. Thatwould point towards continued drought conditions for the region andmost likely some worsening. As noted a few weeks ago, the NWS 30 dayoutlook valid for January 2009 had us in above normal rainfall. Well,I'd like to see that happen...really, I would. 18z GFS time seriesthis week for OKC shows RH values AOB 70% all week except for a periodThursday morning into the afternoon at 5Kft (NAM has a little moremoisture). However, the surface is very dry and only expect clouds atthis point. Indeed, Thursday looks quite cloudy per BUFKIT cloud chart.In the dailies, I used the 18z NAM through Tuesday for forecasttemperatures and frontal passages. On Monday we'll see a rapid warmup into the mid 50s prior to a cold front arriving between noon and1pm. After that we cool off into the mid 40s by late afternoon. 18zNAM RH shows enough saturation in the low/mid levels for clouds.Tuesday was a great discussion day as noted earlier. Since myconversations with Andy, the models have significantly cooled the highand I'm going with the 18z GFS at low 40s for Oklahoma City.Wednesday will be in the mid 50s as we warm ahead of the next coldfront. It is this cold front that will bring the most significantchanges of the week. The front is expected Wednesday afternoon. Asthe models typically do not forecast Arctic cold front well, I may gethosed on my forecast high. I have brought the high down a few degreesfrom what I wanted to go (59F). This is an area where the GFS appearsthe best model as it is a few hours ahead of the NAM with the initialwindshift and arrival of cold air. I'm not going as low as GFS BUFKITdata of 51F.After the front, temperatures rapidly drop and stay in the teens onThursday as cold air advection and clouds keep temperatures fromrecovering. The GFS showed this several times last week and I believethis is a good forecast. The ECMWF also shows a decent chunk of thecold air making it into Oklahoma, so confidence is decent on thisforecast. My forecast high for Thursday is 20F and this is goingbelow 18z GFS BUFKIT data. Models are way off on the warming forFriday and I agree with NWS OUN on going in the mid 30s. Saturday maysee a recovery into the upper 40s ahead of the next scheduled coldfront on Sunday. Confidence on Sunday is below normal and the bustpotential is pretty high at D7. I'm going with climo at upper 40s,which is what OUN has.-----------------------------------------------------------------------Comments from Greg Whitworth:I've got a slightly different take on tomorrow's front. It appears a trough will swing through first, turning winds to the northwest with gusts to 30 mph. Fire danger will be high. I think a reinforcing surge (the real front) will come in a few hours later in the evening. Winds should finally lay down going into Tuesday AM, allowing temps to fall back into the lower 20s. I think he's onto something with highs in the low 40s on Tuesday.. I dropped my high 5 degrees already.Wednesday morning looks warmer since winds will remain up out of the south overnight. Should be another trough passage around 10 am Wednesday, followed by the arctic front by mid-afternoon. I too cut below MOS guidance on Thursday and probably not cold enough. I suspect there could be 10s and single digits Friday morning. I also agree there will not be a warm-up Friday as the GFS had the high in the wrong place (but corrected it some on the 0Z run tonight). If winds are south instead of southwest, there could be a plume of deep moisture from Texas come up and overrun the cold air. This would lead to drizzle and possibly some freezing drizzle Saturday morning. It appears a large trough/warm front will move off the Rockies and try to displace the cold air on Saturday. I'm buying this solution at this time. Keep your eye on the following Tuesday.. could be near record warm if all pans out.I'm keeping my eye on a system scheduled to arrive around the 23rd or 24th as it appears the western ridge may break down long enough to allow a southern system to come across. It may be moisture deprived though.
My numbers were..OKC 32/55 23/45 32/56 18/25 10/35 34/55 32/46 24/55 33/66 39/46 27/35 32/47All pops zero.