textproduct: Columbia

SYNOPSIS

Typical summertime weather is expected to continue into the start of the work week, with near to slightly above normal temperatures and daily shower and thunderstorm chances. Showers and thunderstorm chances ramp up for Tuesday and Wednesday as a weak front enters the Southeast. More isolated to scattered convection expected for the second half of the week.

NEAR TERM /UNTIL 6 AM TUESDAY MORNING/

Key Message(s):

- Seasonal pattern expected to continue, with warm temps and scattered showers/storms expected.

The pattern remains largely unchanged compared to yesterday, so a persistence forecast is in order across the area. Ridging remains in place across the southeastern US, though it is fairly weak compared to what we were dealing with last week. This is probably amplifying slightly as a late season trough digs through the OH and TN Valley region towards us today. PWs are in the 1.7"-1.9" across the area, with MLCAPE of generally 1000-1500 j/kg. TEI and DCAPE are near the thresholds of what you'd expect for sub-severe convection to be the primary threat for the most robust convection this afternoon. Expecting coverage to generally be similar to what it was yesterday with scattered showers and storms dotting the skies and moving very slowly. This is largely driven by the aformentioned ridging across the area, with RAP, REFS, and HRRR forecast soundings all showing evidence of weak subsidence aloft near the 500 hPa layer. So while convection is favored, especially if the sea breeze works its way up here or along outflow boundaries, overall coverage should still remain isolated to scattered. Highs today are expected to be seasonal in the low 90s. Convection is expected to wane quickly beyond sunset as instability dies off. So look for a pretty quiet and warm night with lows in the low 70s across the area.

SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/

Key Message(s):

- Rain chances increase mid-week as a weak front approaches - Rain may be heavy at times with a marginal threat of flash flooding

An upper level trough shift east mid-week allowing for strengthening southwest flow. This will lead to strengthening moisture advection into the Southeast. Mean PWAT values from model ensembles increase to over 2 inches. The strongest forcing for convection will likely remain west of the area through the day on Tuesday. However diurnally driven showers and storms should develop in the warm, moist airmass.

As a weak cold front continues towards the Southeast showers and storms become increasingly likely for Wednesday. Atmospheric moisture continues to increase with the NAEFS mean PWAT values exceeding the 90th percentile across the area. There will be a localized threat of excessive rainfall mainly due to the anomalously high PWATs and long, skinny CAPE profiles typical of a flooding threat. However, storms should be moving fast enough to limit any significant or widespread flooding problems. Synoptic forcing and enhanced convergence at the low levels will allow convection to continue into the evening and overnight periods.

With increased moisture and a breakdown of the ridge, expect highs a few degrees cooler than the previous few days for Tuesday, in the upper 80s to low 90s. Cooler once again Wednesday with highs generally in the mid to upper 80s. Lows for both Tuesday and Wednesday in the low 70s.

LONG TERM /THURSDAY THROUGH MONDAY/

Key Message(s):

- Near normal temps with isolated diurnal convection each day

Global ensembles favor broad troughing over the eastern US through the long term. Weak southerly flow, a decaying frontal boundary and PWAT values near or above normal will support at least a chance of rain each day. The highest values will be nearer the coast where moisture is deeper. Temperatures will generally be near normal with highs in the low to mid 90s depending on convective coverage. Nighttime lows will be in the low to mid 70s.

AVIATION /19Z MONDAY THROUGH SATURDAY/

Generally VFR conditions expected through the forecast period outside of convection.

Pattern looks quite similar to what we have seen the last couple of days. Ridging aloft is over the area, helping to suppress widespread convection but generally allowing scattered showers/storms to develop. Expecting these to remain benign but the strongest thunderstorms may produce wind gusts of 25-35 knots if one goes up directly over an airfield (see the storm that impacted CAE yesterday evening). PWs are high, so brief visibility restrictions are likely in any heavy thunderstorm that does move over an airfield. Overall though, VFR conditions are expected to prevail. After the sun sets, the convection will likely diminish in coverage and intensity, with scattered cloud debris remaining across the area into the night. AGS/OGB may see patch ground fog tonight but it seems pretty unlikely to be a problem given that guidance is developing a 20-25 knot low- level jet tonight. By mid-morning tomorrow, there is some indication that large scale forcing + increased low-level moisture ahead of our next front may aid in the development of MVFR cigs as cumulus gets going. There is only a 40ish percent probability of MVFR cigs mid-morning tomorrow in HREF guidance, so left BKN035 by 15z to trend in that direction. More widespread showers and storms are expected towards the end of this period tomorrow, so mentioned VCSH for now with the expectation that thunderstorms will be added as we get closer to the timeframe.

EXTENDED AVIATION OUTLOOK...Patchy ground fog possible each night...but is unlikely to cause significant issues at the terminals. A front will approach the Southeast Tue/Wed leading to increased thunderstorm chances.

CAE WATCHES/WARNINGS/ADVISORIES

SC...None. GA...None.