Thursday Aug 27

Past day verification and analysis: Low of 70 with no precip - I predicted a low of around 70 for the evening forecast/Thursday low... I'm off to a good start.

Synoptic analysis:
Upper level low in the SE will begin to shift eastward today. Chance of afternoon storms today as the dry stream of air lifts north of the region. Danny will approach the Outer Banks Friday afternoon/evening and potentially interact with upper level support to increase storm chances. A cold front will move through Sunday enhancing the chances for Thunderstorm activity. Moisture is limited but available with PW values exceeding 1.2 inches.


Near term (12 hr):

NAM is showing an increased chance of convection later this afternoon centered over the northern piedmont. SBCAPE has already exceeded 2500 J/Kg. Storms will be scattered and unorganized due to a lack of sufficient shear. The stream of dry air in the upper atmosphere has shifted to our north based on water vapor. Initiation of storms looks to be a weak pressure anomaly at the surface based on the latest RUC. This is currently located just west of Winston Salem. Severe winds due to downdrafts are possible this afternoon. NCAPE values are not too impressive but can't rule out small hail and weak downdrafts if storms develop. Will go with climatological chance PoPs for the triangle without mention of severe. Will lower temps slightly due to enhanced cumulus cloud cover this afternoon. No reason not to stick with persistence on the overnight low.


Short term ( 12 -36 hr):
In the short term concentration shifts towards the impact of the deep south upper level low and tropical storm Danny. Current guidance has Danny moving just east of the Carolina coast and northward toward Boston. 12z Nam has the track shifted slightly west. Although... I will strictly follow NHC/HPC guidelines for now. The interesting part is how Danny will interact with the upper low over the deep south which is forecast to shift east. The closed low will lift and become open toward the end of the short term. 500 mb vort max will approach late in the day on Friday. At the same time a zone of convergence could form from the juxtaposition of Danny and southerlies ahead of a low pressure in Indiana. The thinking is that a band of showers and storms will set up near the triangle due to all of these factors.... Therefore will go with greater than climatological chances of precip on Friday. Also, could see bands directly associated with Danny also effect the eastern piedmont. Will go with climatological temps despite southerly winds due to clouds associated with Danny. These clouds also might reduce available convective potential cenergy... but not enough to lower PoPs.


Long term (Beyond 36 hr):
The open wave in the deep south will lift out of the region and focus will shift toward a deepening upper level low near the great lakes which will eventually become closed. Latest model guidance is stronger and more transient with the upper low. The triangle will be under the right entrance region of the upper level jet associated with this closed low. A surface low will move down stream of the upper low and eventually become stacked. A relatively strong trailing cold front for this time of year will approach the region on Sunday afternoon. GFS theta e analysis shows the cold front not moving through until Tuesday afternoon (oh the agony). Therefore the GFS shows storms developing on Sunday and Monday. Not currently confident that the cold front will stall over the region on Monday therefore will only go with slight chance PoPs... but do feel confident that numerous storms will develop on Sunday to warrant likely PoPs. Will go above climatology on Saturday afternoon due to being in the warm sector, therefore enough instability should exist to warrant high chance. Will keep an eye on the severe threat on Sunday as shear and helicity will be enhanced due to better upper level support. Will keep temps at climatology due to increased cloud coverage. After cold front moves through expect dry and cooler conditions.


Forecast:

Wednesday afternoon: 30% chance of storms. Precip less than .1 inch except higher in storms. High 93

Thursday night: 30% chance of showers and storms before 10 PM. Low around 70.

Friday: 50% chances of storms mainly after 2 PM. 40 % chance of storms through the night. High 87 Low 72 precip .25 inches

Saturday: 30% chance of storms in the afternoon. High 88 low 71. precip less than .1 inches

Sunday: 60% chance of storms mainly after 2 pm. high 86 low 71. precip .3 inches

Monday: 30% chance of storms mainly after 2 pm. high 85 low 68. precip less than .1 inches

Tuesday: Mostly cloudy giving way to sun in the afternoon high 83 low 60

Wednesday: Clear and seasonably cool high 80 low 60

Review of RAH AFD: Near term: I took a look at the sounding but I missed the inversion layer in the mid atmosphere. It looks like that has a good chance to be overcome though. I'll be sure to look for that next time.