Mountain Area Forecast ( Sep 10-12 )

An Alert For Strong & Gusty Winds For Monday Into Tuesday As The Pressure Gradient Tightens With The Inland Movement And Weakening Of Hurricane Irma

Strong and gusty winds are expected to develop at high elevations by the overnight-morning hours of Monday, then increase across middle-lower elevations by later Monday into Tuesday morning.  

Wind speeds of 20 to 40 mph are expected at elevations below 2700 feet, with 40 to 60 mph, or locally higher in gusts ( along mountain ridges and in high gaps ), at elevations above 2700 to 3000 feet.

Overnight Into Sunday Morning

Clear.  Chilly.  Large vertical temperature difference between colder mountain valleys and milder ridges.  Winds E-SE at 5-15 mph, with some higher gusts, along mid-upper elevation mountain ridges.  Temperatures varying from 30s within colder mountain valleys to the upper 40s to low 50s on exposed ridges.  Areas of dense river valley-lake fog.

Sunday Afternoon

Mostly sunny.  Pleasant.  Winds ENE-E at 5-10 mph, with some higher gusts along mountain ridges.  Temperatures varying from the low-mid 60s at upper elevations to the lower-middle 70s.

Sunday Night Into Monday Morning

Increasing high clouds overnight into morning.  Increasing winds at high elevations.  Winds E-ESE at 10-20 mph, with higher gusts, along mid-upper elevation mountain ridges.  Wind gusts near 40 mph at highest elevations by sunrise. Temperatures varying from the 40s to low-mid 50s.

Monday Afternoon

Mostly cloudy.  Showers developing.  Winds ENE-ESE at 10-20 mph, with higher gusts, at elevations below 2700 feet.  Winds ENE-ESE at 20-30 mph, with gusts over 40 mph, on mid-upper elevation mountain ridges.  Cool with temps mainly in the 50s to lower 60s ( coolest upper elevations where cloud bases will lower ).

Monday Night Into Tuesday Morning

Rain showers.  Downpours possible, especially along the windward slopes-crestlines of the High Knob Massif and Tennessee Valley Divide.  Windy.  Winds ENE to E at 15-25 mph, with higher gusts on mountain ridges-plateaus, below 2700 feet.  Winds ENE-ESE at 25-35 mph, with gusts of 40-60 mph, at elevations above 2700-3000 feet.  Low clouds with widespread dense fog at upper elevations.  Temps varying from around 50 degrees at high elevations to the mid 50s to lower 60s.

An initial surge of rain from the remnants of Irma will impact the mountain region late Monday into Tuesday, then a possible break for a prolonged period may occur until rain chances increase again during mid-late next week for locations west and northwest of the Blue Ridge province.

Rainfall amounts are expected to vary widely across the southern Appalachian region.  Heaviest totals are expected to fall along the Blue Ridge, from the Meadows of Dan southwest through western North Carolina.  Least amounts are expected near and northwest of the Virginia-Kentucky state line, and within portions of the Great Valley of eastern Tennessee, where totals of 0.50-1.00″ or locally less are most likely on downsloping winds.

Rainfall totals of up to 3.00″ to 6.00″+ are expected along the Blue Ridge in southwestern-western North Carolina.  Max rain amounts are likely near Lake Toxaway, Nc., with other enhanced totals in the Mount Mitchell ( Black Mountains ) and Grandfather Mountain areas.  Secondary maximums of up to 1.50-2.50″+ will be possible in the High Knob Massif-Black Mountain corridor of southwestern Virginia on upsloping low-level air flow.

 

Weather Discussion ( All About Irma )

For the fourth consecutive night temperatures are in the 30s amid colder mountain valleys of the High Knob Massif, with low 40s here in Clintwood ( 42.8 degrees at 4:00 AM ).

This weather period will be all about the approach and inland movement of destructive and powerful Hurricane Irma.  Although passing far southwest of the Mountain Empire, the pressure gradient will initially become so strong that impacts can not be escaped.

Irma has regained CAT 4 status after weakening along the coast of Cuba following interaction of its circulation with hilly to mountainous terrain.  Pressure has dropped back down to 928 mb as of 4:00 AM Sunday.  An additional gain in strength will be possible over very warm water today.

The track forecast has continued to ease west to place the entire Gulf Coast of Florida in a grave position through coming hours of Sunday into early Monday.

Most models are now taking the remnant low into western portions of Kentucky and Tennessee as it becomes extra-tropical, with possible subsequent movement back to the east-northeast during mid-late this week.

Any flooding rains are most likely along the Blue Ridge where strong orographic lift will enhance amounts late Monday into Tuesday ( I will not be surprised to see up to 10.00″+ in the Lake Toxaway and Highlands area of south-western North Carolina where tropical moisture will be initially lifted upward into the higher elevations on very strong upslope flow ).

Although no flooding is expected, local rain amounts could vary significantly from a max over the high country of the High Knob Massif to low amounts along the Kentucky side of the border on strong downsloping E-SE air flow.  Some places along the Virginia-Kentucky border may pick up the most rain later this week when air flow shifts southwest and whatever is left of Irma’s extratropical low moves eastward toward the lower Ohio Valley.

Meanwhile, strong & gusty winds will develop Monday and Tuesday ( first at high elevations before mixing downward into middle-lower elevations ).  Local power outages can not be ruled out until the remnant low fills and the very strong pressure gradient weakens into mid-week.