Massanutten Resort / Harrisonburg

Harrisonburg, VA

Currently

Temperature 84°F
Feels Like 87.6°F
Humidity 41%
Pressure 1012mb
Wind 14.97mph from the SW
Scattered clouds 84°F Scattered clouds
This Afternoon Isolated Showers And Thunderstorms
High: 87°F Low: 71°F
Monday Sunny
High: 79°F Low: 59°F
Tuesday Sunny
High: 83°F Low: 69°F
Wednesday Mostly Sunny then Chance Showers And Thunderstorms
High: 89°F Low: 70°F
Thursday Chance Showers And Thunderstorms
High: 81°F Low: 65°F
Summary

SYNOPSIS

... A cold front will approach from the northwest today and move through by Monday morning. High pressure briefly returns Tuesday before another cold front crosses the area Wednesday and Thursday.

NEAR TERM /THROUGH TONIGHT/... MORNING UPDATE: A very warm start to the day already with temperatures already well into the 80s for most. Dew points in the upper 60s to low 70s already have heat indices in the 90s as well. This is the mark of a truly hot air mass, with very little overnight relief. Current analysis from the 12z IAD RAOB and ACARS data depict steep lapse rates off the deck just above the eroding inversion, with very dry air up at around 700mb. Satellite continues to show some upper-level clouds streaming in from the west. This may play a pivotal role in the forecast later on today.

Heat: The thickness and duration of cloud cover today could greatly affect temperatures, although most guidance suggests highs in the mid to upper 90s remain likely. A surface trough near the Blue Ridge will should higher dew points to pool to the east, which will lead to heat index values around 102-107. A few counties along the Shenandoah River were added to the Heat Advisory earlier this morning since even a somewhat conservative forecast would result in peak heat index near 100 (the lower criteria west of the Blue Ridge). Dew points should mix down pretty efficiently today however, and that paired with clouds potentially limiting temperatures could bring these numbers down a few degrees. But that is a low certainty occurrence at this time, so holding firm on the previous forecast for now.

Generally speaking, not enough data is in to change much in regards to the severe/flood sections below. Early indications from hi-res guidance show very sparse coverage this afternoon due to a strong capping inversion that remains present throughout the day. This could really reduce the severe weather threat, which is alluded to in the sections below.

PREVIOUS DISCUSSION: Thunderstorms/severe weather: Several different scenarios could play out with thunderstorms today, with little model convergence on any one solution, and some potential for multiple rounds. The next ripple in the flow could result in some isolated showers west of the Blue Ridge through the morning. As it intersects the surface trough and greater moisture this afternoon, scattered storms could intensify toward the I-95 corridor. However, forecast soundings show a stout cap around 10kft with a very dry layer of air just above it. So it's completely possible this round never develops or produces only anemic updrafts. Meanwhile, storms will develop closer to the actual cold front in the Ohio Valley. Some of these storms could survive across the Appalachians this evening. Or, new convection could develop as greater forcing moves into the area and the previous cap erodes somewhat, with the atmosphere still being rather unstable despite the time of day. Guidance does indicate the potential for at least some scattered showers and storms to be moving across the area for a good part of the night, although there are solutions where most convection dissipates during the evening, meaning many locations could miss out on seeing rain altogether. Regardless of what scenario materializes, increased flow aloft will result in around 30 kt of deep shear, which could lead to storm organization. Instability will be largely driven by the hot and humid airmass with poor mid level lapse rates indicated. The main hazard will be damaging wind gusts.

Flash flood threat: There is little guidance support for excessive rain totals, which combined with the current dry conditions, suggests the threat for flash flooding is low. However, we'll have to be cognizant of the airmass east of the Blue Ridge with precipitable water values near 2 inches and a nearly unidirectional low level wind field that could promote back building. Any threat would likely be confined to sensitive urban areas.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... By Monday morning, the surface cold front will be nearly through the area, with any lingering showers and storms quickly exiting southern Maryland. While temperatures will still be a little above normal in the mid 80s to near 90, dew points falling into the 50s and a gusty northwest wind will likely feel refreshing compared to the weekend. A few showers may linger through midday along the Allegheny Front as the primary upper trough axis passes. As the wind abates Monday night, lows will range from the mid 50s in the mountains to 60s in most other places.

The surface high will translate through on Tuesday and move to the southeast Tuesday night. Comfortable dew points in the mid to upper 50s remain through the day, although temperatures will rebound a little to the upper 80s and lower 90s. A light southerly flow and potential clouds will result in a slightly warmer night. There is a slight chance weakened convection from the Ohio Valley makes a run at the Appalachians toward Wednesday morning.

LONG TERM /WEDNESDAY THROUGH SATURDAY/... The synoptic pattern becomes more amplified over the CONUS heading into Wednesday as an upper shortwave moves into the Great Lakes and Mid-Atlantic. S/SW flow ahead of this feature will bring warm, humid air from the south into the region, with high temperatures reaching into the upper 90s with dewpoints in the 60s to low 70s. As the cold front associated with the shortwave moves through, showers and t- storms are likely, though depending on the timing of the front. As of now, timing appears to be Wednesday afternoon and evening, with some shower activity possibly lingering into Thursday. Temperatures lower behind the cold front Thursday into the 80s to low 90s, but dewpoints look to remain in the mid 60s.

A quick-moving area of high pressure passes to our north on Friday. Mostly dry conditions are expected, but a few showers are possible as the center of high pressure swiftly moves offshore by the evening and minor perturbations pass by aloft. Temperatures will be in the 80s to low 90s.

Saturday is less certain, depending on another area of low pressure moving into the Great Lakes. Some shower activity is possible if the associated warm front works into our area, but PoPs are currently around 20-30% leaning towards our western zones.

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