Sugar Mountain

Forecast Discussion

Summary

SYNOPSIS

... A frontal system will push through the forecast area tonight into Tuesday. Cold high pressure will gradually build in behind this system with a return of below normal temperatures through the week. Widespread rain is likely Friday into Saturday as a low pressure system tracks north from the Gulf of Mexico.

NEAR TERM /THROUGH TONIGHT/... As of 250 AM EST: Water vapor satellite imagery shows a low amplitude trough moving over the southern plains early this morning, with high clouds ahead of this feature streaming into the area from the area from the west. Meanwhile, the GOES-East nighttime microphysics imagery depicts lower clouds affecting mainly locations along and southeast of I-85. In addition, the numerical models indicate a brief period of moist, low-level upglide affecting piedmont areas southeast of Charlotte through the early morning hours before moving east by daybreak. Will advertise some low chance PoPs for showers in these areas before the 12Z. Otherwise, the bulk of the area will be dry today, with temperatures climbing into the 60s east of the mountains and also in the lower mountain valleys, with insolation spoiled only by high clouds at times.

The mesoscale models have showers building ahead of the approaching cold front along the spine of the southern Appalachians toward sunset. The vorticity associated with the plains upper shortwave will cross the southern Appalachians circa 06Z, along with a better, but brief, period of upper jetlet divergence. This will warrant a narrow window of likely PoPs for rain showers along the higher elevations around the Smokies. Very little shower activity should survive east of the mountains tonight as 850 mb flow quickly veers westerly atop the passing cold front. Any mixover to snow showers in the post-fropa cold advection late tonight should be confined to the highest elevations - with accumulations very light.

SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 205 AM EST Monday: The upper-level flow becomes more meridonal on the front side of a building ridge after a h5 trof axis crosses east of the FA early Tue afternoon. Moist llvl upslope flow will continue to support -shra/-snsh across the wrn NC mtns early Tue with little additional sn accums over the higher peaks before a cP airmass begins mixing in from the northwest. A Canadian sfc high will build in Tue afternoon and CAA in the h92-h85 layer is rather pronounced based on sigma winds which will help keep max temps below normal by a few degrees. The thickness scheme supports m60s over the non/mtns...but it doesn/t account for advection...so will side with the lower-end guidance. Mins drop off below normal Tue night in good rad cool...so max temps on Wed will struggle to reach the m50s non/mtns and arnd 50 F mtn valleys even in very good insol. Another dry cP sfc high reinforces the cool pattern Wed evening and begins to develop a wedge east of the Apps thru the period. Thus...another cold night is in store with mins dropping abt 8 degrees F below normal.

LONG TERM /THURSDAY THROUGH SUNDAY/... As of 315 AM EST Monday: Not too many changes were made to the ext fcst. Thu still looks like a dry day as a 1036 mb sfc high centers over the northeast and builds a strong wedge across the FA. A h5 s/w associated with split upper flow will be well southwest of the area during this time...so a dry forecast with max temps a couple cats below normal still seems reasonable. The overnight period will see temps drop well below normal yet again and by that time cyclogenesis will commence across the nw/rn GOM.

This is when the models begin to differ sigfnt/ly wrt the synoptic pattern. The GFS develops a weak Atl coastal low and swings the energy northeast over the weekend...while the ECMWF has trended farther west with it/s low...now progged to track up the Apps like a Miller B. The CMC is in the middle somewhat yet favors the GFS. In any regard...sfc temps will be cold enuf across the higher terrain early Fri for some -snsh or wintry mix with little accums by the time strong WAA kicks in by the afternoon.

The majority of guidance indicates a non/diurnal temp curve Fri night which makes sense considering the degree of llvl WAA...so have abv freezing temps all areas thru the overnight and no wintry precip. This warmer scenario could change as the overall pattern remains quite uncertain. Sat shud slowly dry out as the low remains progressive...yet wrap-around NC mtn -shra/snsh would be likely into Sun morning. Max temps Fri will remain quite cold with a strong wedge maintained by evapo cooling and increasing precip. Highs will probably remain in the 40s most locales. Max temps Sat are tricky due to the timing of the wedge breakdown and pattern evolution...but for now have generally l50s north and u50s south.