Winter Weather Discussion for February 1-2, 2011.
– Widespread winter weather is possible during the valid period. Precipitation types are likely to range from a cold rain early Tuesday in southeast Oklahoma to snow in the northwest/panhandle. Transition to all freezing/frozen precipitation will occur during the morning hours on Tuesday.
Models remain at odds with each other and intra-model runs including medium range ensemble outputs. However, there is some agreement this evening on the widely discussed winter weather potential for early next week. Concern and confidence regarding a medium-end event is increasing. A high-end event cannot be ruled out.
00z NAM is much colder than prior runs and the 18z GFS seems to collaborate this shift. Additionally, these two runs are in good agreement on the track of the upper system through 84 hours (end of NAM run). Given that the cold air now appears to blast into Oklahoma Tuesday morning and coincide with the onset of precipitation, only a brief instance of cold rain is expected across central Oklahoma. This should transition to freezing rain in OKC/TUL by 1-2am Tuesday morning. NAM transitions to sleet by 7am in these areas. The upper system will still be well west of the region and continued precipitation is likely during the morning hours on Tuesday. 18z GFS inexplicably shuts down precipitation by noon Tuesday across much of Oklahoma. I’m not convinced this is a good solution given RH values near 100% across much of Oklahoma. The 00z run will certainly be interesting.
Despite the early shutdown of precipitation on the GFS, there is sufficient QPF to warrant a medium-end event should it be anything other than rain. However this model held the warm air in-place longer than what is seen on the new NAM keeping frozen/freezing precipitation limited. Time of year and presence of 0F temperatures in central Canada provides confidence in the expected cold air. Ground temperatures are seasonably cool in the 40s and will provide little to no resistance to expected precipitation rates/accumulations.
Long story short, the full spectrum of precipitation types remain on the table this forecast and not a shocker for the first issuance. The primary players appear to be at said table: cold air, moisture, and lift. Another significant concern is wind speeds on the backside of the surface low. 18z GFS shows 20-25mph Tuesday evening. This could be a major factor if ice is present on power lines. That being said and as noted above, confidence in a medium-end event is also present and discussions are initiated. Next discussion should be out by late Saturday.by