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Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260622_1200
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 06/22 12Z 0.24 2307 84 53 9 0.00
Mon 06/22 13Z 0.25 2207 82 50 10 0.00
Mon 06/22 14Z 0.32 2107 82 43 10 0.00
Mon 06/22 15Z 0.46 2106 80 46 10 0.00
Mon 06/22 16Z 0.31 2006 75 62 10 0.00
Mon 06/22 17Z 0.28 1809 76 79 10 0.00
Mon 06/22 18Z 0.34 1911 82 95 10 0.01
Mon 06/22 19Z 0.20 1911 89 95 9 0.07
Mon 06/22 20Z 0.14 1814 93 96 9 0.15
Mon 06/22 21Z 0.12 1817 96 96 9 0.13
Mon 06/22 22Z 0.08 1717 94 93 9 0.06
Mon 06/22 23Z 0.08 1617 89 95 9 0.01
Tue 06/23 00Z 0.12 1518 89 97 9 0.02
Tue 06/23 01Z 0.14 1517 93 99 9 0.03
Tue 06/23 02Z 0.16 1517 95 96 10 0.05
Tue 06/23 03Z 0.13 1517 97 98 10 0.04
Tue 06/23 04Z 0.12 1517 97 94 11 0.04
Tue 06/23 05Z 0.10 1617 98 94 11 0.03
Tue 06/23 06Z 0.12 1713 98 93 11 0.03
Tue 06/23 07Z 0.08 1709 99 87 12 0.02
Tue 06/23 08Z 0.05 1605 99 87 12 0.02
Tue 06/23 09Z 0.04 1504 99 92 12 0.01
Tue 06/23 10Z 0.05 1303 99 95 12 0.01
Tue 06/23 11Z 0.04 1301 99 95 11 0.01
Tue 06/23 12Z 0.04 3401 99 89 11 0.01
Tue 06/23 13Z 0.05 3304 99 87 11 0.00
Tue 06/23 14Z 0.06 3407 98 84 11 0.00
Tue 06/23 15Z 0.06 3509 97 77 11 0.00
Tue 06/23 16Z 0.06 3510 95 60 10 0.00
Tue 06/23 17Z 0.04 3510 94 52 10 0.00
Tue 06/23 18Z 0.03 3511 92 38 10 0.00
Tue 06/23 19Z 0.03 3511 90 23 10 0.00
Tue 06/23 20Z 0.06 3512 88 15 11 0.00
Tue 06/23 21Z 0.07 3513 84 10 11 0.00
Tue 06/23 22Z 0.07 3515 79 7 11 0.00
Tue 06/23 23Z 0.06 3516 74 6 11 0.00
Wed 06/24 00Z 0.09 3418 77 7 11 0.00
Wed 06/24 01Z 0.11 3420 82 10 10 0.00
Wed 06/24 02Z 0.08 3421 87 10 10 0.00
Wed 06/24 03Z 0.03 3421 87 11 10 0.00
Wed 06/24 04Z 0.07 3521 88 14 10 0.00
Wed 06/24 05Z 0.05 3521 89 17 9 0.00
Wed 06/24 06Z 0.08 3522 88 16 9 0.00
Wed 06/24 07Z 0.10 3521 85 17 9 0.00
Wed 06/24 08Z 0.07 3520 84 20 9 0.00
Wed 06/24 09Z 0.04 3419 82 18 9 0.00
Wed 06/24 10Z 0.14 3320 81 17 9 0.00
Wed 06/24 11Z 0.22 3221 82 21 9 0.00
Wed 06/24 12Z 0.29 3221 84 22 8 0.00
Wed 06/24 13Z 0.33 3221 85 26 8 0.00
Wed 06/24 14Z 0.41 3120 85 27 8 0.00
Wed 06/24 15Z 0.59 3119 84 30 8 0.00
Wed 06/24 16Z 1.10 3017 87 37 8 0.00
Wed 06/24 17Z 1.68 2916 90 38 8 0.00
Wed 06/24 18Z 3.21 2816 87 36 8 0.00
Wed 06/24 19Z 5.04 2816 85 44 9 0.00
Wed 06/24 20Z 6.72 2816 82 44 9 0.00
Wed 06/24 21Z 6.37 2917 80 41 9 0.00
Wed 06/24 22Z 3.71 2919 85 34 9 0.00
Wed 06/24 23Z 1.86 3020 86 30 9 0.00
Run total areal avg QPF for the Central_Greens is: 0.75 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