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Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260629_0000
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 06/29 00Z 0.08 3410 60 43 14 0.00
Mon 06/29 01Z 0.07 3513 57 39 14 0.00
Mon 06/29 02Z 0.23 0115 52 37 14 0.00
Mon 06/29 03Z 0.38 0215 52 38 14 0.00
Mon 06/29 04Z 0.45 0314 55 45 13 0.00
Mon 06/29 05Z 0.40 0411 58 53 13 0.00
Mon 06/29 06Z 0.31 0309 57 61 13 0.00
Mon 06/29 07Z 0.22 0308 55 60 13 0.00
Mon 06/29 08Z 0.13 0106 55 57 13 0.00
Mon 06/29 09Z 0.12 0107 55 52 13 0.00
Mon 06/29 10Z 0.16 0108 57 44 13 0.00
Mon 06/29 11Z 0.13 0008 59 37 13 0.00
Mon 06/29 12Z 0.10 0008 60 25 13 0.00
Mon 06/29 13Z 0.10 0008 62 16 13 0.00
Mon 06/29 14Z 0.14 3506 65 13 13 0.00
Mon 06/29 15Z 0.25 3404 67 16 13 0.00
Mon 06/29 16Z 0.26 3304 65 25 13 0.00
Mon 06/29 17Z 0.38 3205 64 39 13 0.02
Mon 06/29 18Z 0.61 3205 61 33 14 0.01
Mon 06/29 19Z 0.64 3204 57 22 14 0.00
Mon 06/29 20Z 0.84 3205 54 17 14 0.00
Mon 06/29 21Z 0.56 3105 53 27 14 0.00
Mon 06/29 22Z 0.30 3104 52 29 14 0.00
Mon 06/29 23Z 0.26 3104 52 26 14 0.00
Tue 06/30 00Z 0.30 3005 54 17 14 0.00
Tue 06/30 01Z 0.38 2904 56 15 14 0.00
Tue 06/30 02Z 0.50 2705 58 16 14 0.00
Tue 06/30 03Z 0.49 2405 59 13 14 0.00
Tue 06/30 04Z 0.66 2307 60 12 14 0.00
Tue 06/30 05Z 0.74 2409 61 14 14 0.00
Tue 06/30 06Z 0.83 2411 61 18 14 0.00
Tue 06/30 07Z 0.86 2413 61 23 14 0.00
Tue 06/30 08Z 0.79 2415 59 27 14 0.00
Tue 06/30 09Z 0.82 2416 59 44 14 0.00
Tue 06/30 10Z 0.79 2416 65 51 14 0.00
Tue 06/30 11Z 0.77 2517 72 50 14 0.00
Tue 06/30 12Z 0.78 2519 79 46 14 0.00
Tue 06/30 13Z 0.72 2419 85 38 14 0.00
Tue 06/30 14Z 0.78 2519 87 44 14 0.00
Tue 06/30 15Z 0.71 2516 90 90 14 0.02
Tue 06/30 16Z 0.39 2312 82 93 14 0.05
Tue 06/30 17Z 0.40 2313 87 97 14 0.02
Tue 06/30 18Z 0.45 2314 95 87 15 0.03
Tue 06/30 19Z 0.49 2217 91 72 15 0.00
Tue 06/30 20Z 0.61 2218 89 78 16 0.00
Tue 06/30 21Z 0.68 2220 94 81 16 0.00
Tue 06/30 22Z 0.70 2222 94 83 16 0.00
Tue 06/30 23Z 0.79 2325 94 94 16 0.00
Wed 07/01 00Z 0.74 2326 94 88 17 0.06
Wed 07/01 01Z 0.83 2328 94 78 17 0.04
Wed 07/01 02Z 0.80 2330 97 80 18 0.05
Wed 07/01 03Z 0.91 2432 97 70 18 0.10
Wed 07/01 04Z 0.85 2630 97 42 18 0.10
Wed 07/01 05Z 0.74 2727 96 35 18 0.05
Wed 07/01 06Z 0.64 2823 93 52 18 0.08
Wed 07/01 07Z 0.67 2725 85 68 18 0.25
Wed 07/01 08Z 0.54 2822 83 42 19 0.09
Wed 07/01 09Z 0.59 2724 90 26 19 0.01
Wed 07/01 10Z 0.61 2825 94 11 18 0.01
Wed 07/01 11Z 0.58 2925 95 5 18 0.02
Run total areal avg QPF for the Central_Greens is: 1.01 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