October 25, 2018
this Thursday night
911 PM EDT
-- Big, COLD RAIN EVENT coming for Richmond Friday & Friday night, 10/26 --
-- Deepening surface low glides up the East coast, driving an over-running rain event --
Let's have a look at the forecasting QPF model amounts for this next rain-maker coming through Richmond on Friday, October 26, through Friday night, and early Saturday morning. It does look like a goodly amount of rainfall. Here's what forecasting numbers show:
*** Centered on Richmond, VA, for Friday & Friday night, 10/26 *** :
Nam -->> 1.50" of rainfall
Gfs -->> 1.33" of rain
C-Gem -->> 1.29" of rain
ECMWF -->> 0.81" of rain, later onset time, Friday afternoon; later finishing time, Saturday afternoon.
WRF -->> 1.25" to 1.50" of rainfall; start 10 AM continue rest of day & night, Friday PM & night. Heavier rain in Richmond between 3 PM and 9 PM Friday PM and night, but light rain continues overnight; Heaviest South of Richmond.
UKM -->> Not avail. 12Z, Thurs.
NavGem -->> 1.32" of rain
This gives an average total rainfall amoungst 6 models above to be 1.27" of rainfall for Richmond, starting late Friday morning, continuing Friday afternoon, evening, & through late overnight Friday night, 10-26. As cited earlier, few forecasting models continue rainfall in to early Saturday morning, before tapering, but the residual, left-over rain Saturday morning should be light.
Precipitable Water values escalate from 0.84" 11 AM Friday upwards to 1.47" late Friday night at 11 PM, with the highest surge of moisture entering our Richmond area during the evening & 1st half of Friday night. This is when I expect rainfall to be heaviest is Friday evening hours in to Friday night, coincident with rising Precip Water values and an increasing LLJ at 850 mb, growing from Southerly at 25 kts, 5 PM Friday up to a peak of 40-45 kts, from the Southeast at height of 5K ft, 11 PM that night. So, I'd suspect this timing to correlate to heaviest rainfall.
Come look with me at Mos data, and you'll see that we remain entrenched in the COLD sector airmass Friday afternoon & night, with temperatures running mid 40's to low 50's at the time the elevated LLJ from the South-Southeast arrives. LLJ = Low-level jet maximum for Friday night.
Surface Level -- The surface low starts near the Southeast Georgia, South Carolina border at 5 PM Friday, North of Savannah, scooting Northeast to near Myrtle Beach by 8 PM, Friday, (29.60"). Then by 2 AM Saturday morning, surface low deepens further to 29.50", still headed Northeastward, located over Northeastern North Carolina, just a jog South of Elizabeth City, NC. 3 hours later, by 5 AM Saturday morning, the surface low takes a left-ward turn Northbound reaching near Virginia Beach, Virginia, 5 AM Saturday morning, at 29.45". The surface low continues its track up the Delmarva peninsula the rest of Saturday morning.
I tried to insert JPG simple picture illustrations of PW mappings, LLJ mapping, surface low position, and Skew-T sounding profile, but this forum board seems to be 20 yrs. old and can't accommodate these simple static illustrations, even when they're under the file limit size. Too bad!
-- cyclogenesis
