GFS EXPERIMENTAL Froude Number for the Green Mountains

Severe Weather and Heavy Rain from the Mid-South to the Mid-Atlantic; Building Heat in the West

Severe thunderstorms may bring damaging winds, a couple of tornadoes, and heavy rain across portions of the Mid-Atlantic into the Mid-South. Severe storms may produce hail across the northern/central High Plains. Hazardous heat will linger across the southern U.S. and build across the West through mid-week. Fire weather concerns continue for Interior Alaska and the Four Corners region. Read More >

Subject: GFS EXPERIMENTAL Froude Number for the greens Model run: BTV_GRID_D2D_GFS_20260622_0600 Using the MB925 to MB850 layer. Assumes greens are orthogonal to 270 degree winds. 925-850 mb Layer Average Wind/RH. Avg QPF over the greens. Date Time Wind RH% 700 850T QPF Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in) === ===== === ==== ==== === === === ==== Mon 06/22 06Z 0.23 2806 70 52 10 0.00 Mon 06/22 09Z 0.25 2407 77 50 9 0.00 Mon 06/22 12Z 0.23 2308 75 47 9 0.00 Mon 06/22 15Z 0.22 2206 74 35 9 0.01 Mon 06/22 18Z 0.44 2111 72 74 9 0.01 Mon 06/22 21Z 0.15 1910 84 92 8 0.12 Tue 06/23 00Z 0.16 1510 89 99 8 0.13 Tue 06/23 03Z 0.18 1512 93 97 9 0.08 Tue 06/23 06Z 0.06 1608 97 95 9 0.04 Tue 06/23 09Z 0.05 3002 98 96 9 0.02 Tue 06/23 12Z 0.03 3506 97 90 9 0.00 Tue 06/23 15Z 0.05 3507 94 38 8 0.01 Tue 06/23 18Z 0.23 3408 82 21 9 0.01 Tue 06/23 21Z 0.52 3312 67 29 11 0.00 Wed 06/24 00Z 0.35 3315 65 40 10 0.00 Wed 06/24 03Z 0.38 3316 70 38 10 0.00 Wed 06/24 06Z 0.23 3315 69 41 10 0.00 Wed 06/24 09Z 0.30 3213 75 33 8 0.00 Wed 06/24 12Z 0.33 3113 80 28 8 0.00 Wed 06/24 15Z 1.40 3014 72 24 7 0.00 Wed 06/24 18Z 1.95 3016 62 53 9 0.00 Wed 06/24 21Z 1.37 3117 70 53 9 0.01 Thu 06/25 00Z 0.80 3118 76 51 9 0.00 Thu 06/25 03Z 0.44 3213 75 52 9 0.00 Run total areal avg QPF for the greens is: 0.44 inches. Froude Number (Frd#): Frd# < 0.5 Flow is subcritical and blocked. Upslope clouds/precip backed farther upwind of and up to mtn crest. W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes. Gap winds possible. Frd# 0.5-1 Flow is subcritical/slow moving/blocked. Upslope clouds/precip falls immediately upwind of mtn crest. W Upslope snow favors western slopes to the Green Mt. spine including: Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln. Gap winds possible. Frd# 1-2 Flow is critical. With strong winds, Mountain waves/downslope winds possible. Precip falls close to mountain ridge crests and on lee side. W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom. Froude > 2 Flow is supercritical/unblocked(rapid flow). Air flows freely over terrain. Persistent upslope snow not favored. Scattered snow showers and flurries. Relative Humidity (RH): 925-850 mb RH > 90% needed for upslope precipitation. with 700mb RH > 70% favors upslope snow. with 700mb RH > 90% greater amounts of W upslope snow possible. 850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1) T > -11 10-15:1 T -11 to -15 25-35:1 T < -15 15-20:1