... High pressure continues to dominate the forecast through Monday. A weak cold front will drift into the region from the north by Tuesday then linger or stall near the North Carolina...Virginia border through midweek as strong high pressure builds across the Midwest. Dry and mild conditions through Monday will give way to scattered to numerous showers and thunderstorms during the later half of the week along with increasingly warm and humid conditions.
NEAR TERM /THROUGH MONDAY/... As of 130 PM EDT Sunday...
High pressure continues to dominate the forecast bringing mostly sunny, dry, and warm weather. Since about 14Z a cumulus deck has been building across a majority of the CWA. Nothing further is expected to develop with such dry air in place and no driving force to push updrafts beyond the LCL.
Based on how fast temperatures have warmed through the AM, most areas besides elevation above 3500 feet were bumped up a degree for likely a slightly warmer afternoon than originally forecast. Despite the dry air in place, such saturated soil conditions mean that any real surface heating is going to be limited some from latent heat restrictions.
Tonight, looking at how lows performed last night, I am running slightly warmer than originally thought. Areas where upper level clouds weren't present were ~2 degrees above forecast. This is again likely due to the ample soil moisture fighting effective cooling despite the dry airmass in place.
Looking ahead to tomorrow, it looks to be a near repeat from today. High pressure to our northwest will be slowly slipping eastward. Overall, the main change in weather will be slightly lower winds and more westerly flow for the western slopes by the afternoon.
SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 155 PM EDT Sunday...
The week will start on a quiet and cool note as a large area of Canadian high pressure drifts slowly southeast from the Ohio Valley across the region and off the Mid-Atlantic coast by Tuesday. Unseasonably cool morning temperatures in the 40s can be expected Tuesday morning, but that should be the end of the cool and dry weather for sometime to come. As the surface high moves off shore and an upper ridge builds to our west, 850mb temperatures will warm from the single digits early in the week well into the positive teens, with even a pocket of +20 flirting with the region as we progress into mid and late week. Humidity levels will also begin to come up through the period.
Tuesday at this point appears to remain dry with high pressure aloft just to the west. A frontal system driven by a short wave riding around the northern periphery of the upper ridge through the Great lakes and into PA/NY, will sag southward to near the MD/WV/VA border late Tuesday. For now, models have held off on bringing any association convection further south than this area as it dissipates trying to move further south into the dry/stable air mass residing over the Mid-Atlantic region.
By Wednesday, the front will slowly sag southward into northern WV/VA and the threat for afternoon/evening development of showers and thunderstorms near the front will begin to increase into at least the chance category. While most of that activity on Wednesday should still remain north of I-64, another area of concern for shower/thunderstorm development will be across the high country of northwest NC and into far southwest VA, where moisture levels begin to increase notably and combined with differential and diurnal heating should lead to scattered afternoon/evening showers/thunderstorms. Still yet on Wednesday, do not see any areas exceeding chance pops just yet.
For temperatures, we will start the week with lows in the 40s and dewpoints in the 30s working our way to highs mainly in the 80s, 70s mountains, by Wednesday. Dewpoints will slowly creep upward into the 50s east and 60s west by Wednesday.
/Confidence in Forecast Parameters/ Temperatures - Moderate to High, Precipitation Probabilities - Moderate, Winds - Moderate to High, Thunderstorm Threat - Low to Moderate.
LONG TERM /THURSDAY THROUGH SUNDAY/... As of 215 PM EDT Sunday...
Weather conditions become more unsettled and problematic during this period as the aforementioned frontal boundary continues to sag southward from daily convective trends. Thursday, the air mass becomes much more unstable and humid as the frontal boundary lingers near the NC/VA border. Scattered to numerous showers and thunderstorms are expected Thursday and at this point appears to be one of the most likely days for thunderstorm coverage. The rainfall amounts and severity still in question at this point, but something that will need to be addressed in future forecasts. The front will linger across the area Friday and Saturday with a continued good chance for showers and thunderstorms. Upper-level conditions become more favorable for convection toward the weekend as a series of short waves move east toward the Mid-Atlantic and also help to break down the ridge.
Another concern that will need to be watched carefully as we move toward the weekend is a tropical system emanating from the western Gulf. The extended range models are all over the place with respect to the location where this will move inland and where it goes after that. The ECMWF has been the most consistent from day-to-day, tracking this system eventually through LA/AR and then turning it northeast into the TN Valley. If so, this could have an additional impact on rainfall and convection in our area by next weekend.
Bottom line enjoy the first half of the week, because the later half certainly appears unsettled and increasingly wet. At least we will have a few days to dry out until we get there.
Temperatures will be a bit above normal during this time frame with 850mb temperatures hovering in the +16C to +19C range for the most part. However, with humidity levels also increasing as well as cloud cover and convection during this period, have tended to drop advertised NBM readings a bit. Highs will generally be in the 70s mountains and 80s elsewhere, nearing 90 across the Piedmont, with lows mostly in the 50s and 60s, mainly 60s to even near 70 during the more tropical later part of the week.