070716 Forecast

Mountain Area Forecast ( July 5-7 )

ALERT For Heavy To Excessive Rainfall At Times From This Week Into Next Week Amid A Persistence Pattern

A heavy-excessive rainfall potential, with the possibility of dangerous flash flooding, will be the main weather concern for locations from the Cumberland Mountains northward in coming days as waves of showers and downpours in storms move across the region.  While many dry hours will occur, accumulative amounts will saturate the ground and make subsequent activity more likely to cause water problems.

It might seem unusual to issue a forecast statement as above, but in this case it is based upon recognition of a repetitive synoptic-scale pattern & recent ( antecedent ) conditions producing numerous flash floods across the region.  It is meant to raise awareness-alert levels that conditions favorable for flash flood generation will be present during a prolonged period of time.

Overnight Into Tuesday Morning

Intervals of showers & downpours in thunderstorms.  Areas of fog.  SSW-SW winds 5 to 15 mph, with higher gusts, along mid-upper elevation mountain ridges & plateaus.  Warm and humid with temps varying in the 60s to lower 70s.

Tuesday Afternoon

Periods of showers & downpours in thunderstorms.  Some storms could be strong to locally severe.  Humid  SW-WSW winds 5-15 mph, with higher gusts.  Temperatures varying in the 70s to lower 80s ( hotter south toward the Tri-Cities ).

Tuesday Night Into Wednesday Morning

A chance of showers & thunderstorms; otherwise, mostly cloudy, hazy and mild.  Areas of fog.  Winds SW-W 5-15 mph along mid-upper elevation mountain ridges and plateaus.  Temperatures widespread in the 60s to near 70 degrees.

Wednesday Afternoon

Hazy & humid.  A chance of showers & downpours in thunderstorms.  Winds SSW-SW 5-10 mph, with higher gusts.  Temperatures in the 70s to low-mid 80s ( hotter south toward the Tri-Cities ).

Wednesday Night Into Thursday Morning

Showers & downpours in thunderstorms.  Winds SW-W 10-20 mph, with higher gusts, mid-upper elevation mountain ridges.  Humid.  Temperatures in the 60s to lower 70s.


Weather Discussion ( July 4-7 )

Reference June 2016 Climate Data for rainfall totals ( more data to come soon ) as well as the new May 2016 Climate Data section.

Strong to severe thunderstorms blasted into the mountains late Monday afternoon with wind damage & power outages in numerous places to accompany downpours of rain.

High Knob Massif Webcam
High Knob Massif Webcam – University Of Virginia’s College At Wise

Rainfall totals topped 1.00″ in Big Cherry Lake basin of the High Knob Massif as the storms developed and moved over into the Clinch and Holston river valleys.

Regional Doppler Composite At 1:18 AM Tuesday - July 5, 2016
Regional Doppler Composite At 1:18 AM Tuesday – July 5, 2016

More downpours of rain are pounding on roof-tops in Clintwood at 1:30 AM Tuesday as new development is propagating northeast from middle Tennessee and the southern portion of Kentucky.

NAM 4 KM Model Total Rainfall Forecast Next 60-Hours ( 1 PM Run )
NAM 4 KM Model Total Rainfall Forecast Next 60-Hours ( 1 PM Run July 4 )

For days now all models have been predicting heavy to excessive rainfall amounts through coming days, with placement & timing of the heaviest rain being the main uncertainty, with each model run being different with  respect to where the flooding rains occur.

The signal; however, is clear.  Heavy to excessive rains are likely to hit in places across the region this week into next week ( European Ensembles continue the pattern into next week ) as a high precipitable air mass hangs over the region.

*Some may think MAX totals of 8″ to 12″ are bogus; however, such amounts were being shown before the West Virginia flood event!
NAM 4 KM Model Total Rainfall
NAM 4 KM Model Total Rainfall Forecast Next 60-Hours ( 8 PM Run July 4 )

In the short-term, models suggest overnight into Tuesday and late Wednesday into Thursday as periods to watch for heavy to locally excessive rain amounts ( this does not mean that activity will not occur in between these waves ).

Due to the nature of convection, and the way it can alter the atmosphere, it will be necessary to update the forecast and this potential for heavy-excessive rainfall through coming days.  The big picture pattern; however, is clear with blazing heat to the south & southwest of the mountain area acting to generate and guide frequent clusters of showers and storms around its periphery into the Appalachians.

The Bottom Line…Now is the time, before the next flood, to be aware that another event or events are possible to likely in portions of the region this week into next week.  While there will likely be many dry hours, the accumulative nature of downpours over time will create the problem ( especially in locales having had 5.00″ or more of June rainfall and 10.00″+ of May-June rain ).

*Any place can flood if too much rain falls too fast, but antecedent rainfall amounts are important to look at with respect to where heavy rain could saturate the ground quicker ( i.e., it will take more rain to cause flooding in locations that were dry during June versus locations which were wet ).