Forecast Discussion
Summary
SYNOPSIS
... High pressure maintains dry and sunny weather through midweek, with valley fog developing each night. A cold front crosses Friday, followed by cooler weather for next weekend.
NEAR TERM /THROUGH TONIGHT/... As of 940 AM Sunday... No updates necessary.
As of 630 AM Sunday...
Dense fog in the river valleys will slowly lift and dissipate after sunrise this morning. An SPS for fog remains in place for the entire CWA through 9 AM. The current near term forecast generally remains on track, with no significant changes needed at this time.
As of 145 AM Sunday...
Calm winds and clear skies are currently facilitating the formation of fog in the river valleys. Fog will continue to increase in coverage early this morning, then gradually dissipate after daybreak. Thereafter, dry and mostly sunny conditions are anticipated for the rest of the day as the eastern half of the country resides under a mid level ridge, and surface high pressure persists across the Ohio Valley and Central Appalachians.
For tonight, high pressure maintains tranquil weather, with river valley fog again likely to develop beneath clear skies.
Temperatures today will be a few degrees warmer than normal, with highs in the upper 70s to low 80s in the lowlands and mid 60s to 70s along the mountains. Overnight lows are then expected to range from upper 40s to 50s.
SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 400 AM Sunday...
High pressure rules the roost surface and aloft this period with mostly sunny days, and clear nights save for the overnight night and early morning dense river valley fog given light flow and warm rivers.
This dry spell comes in concert with the start of the fall fire season across much of the area. Light flow and afternoon RH values in the 50s, and some 40s, should mitigate issues, although the spot brush fire can occur under these conditions.
Temperatures will continue to run above normal, although valleys away from rivers will likely bottom out lower than central guidance at night.
LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 400 AM Sunday...
This period features a pattern change, mainly on temperature but also with an interruption of the dry weather, as a long wave trough amplifies over eastern North America.
A large southern stream upper level low over the western U.S. this morning opens up and lifts northeastward into central Canada through midweek week, ahead of a northern stream short wave trough that then digs southeastward across the high plains, midwest and Great Lakes in its wake. This drives a surface cold toward the area Thursday, and then on across the area on Friday.
There have been two camps on the amplification of this short wave trough over the eastern U.S. during the latter portion of the upcoming work week, and models early this morning are converging on a more amplified solution. This will allow the system to pool and squeeze out more moisture, yielding a higher chance, if not likelihood, of showers across the area on Friday, with mainly afternoon and evening thunderstorms even possible.
This results in a more cohesive long wave trough amplification over eastern North America this weekend, with a stout temperature drop behind the initial cold front. There could be showers underneath the mid-upper level trough, at least during the afternoon and early evening, before high pressure builds in late in the weekend.
Central guidance reflects above normal temperatures through Thursday, and then highs dampened by clouds and showers Friday, and highs and lows dropping below normal over the course of the weekend.