Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260528_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)
=== ===== === ==== ==== === === === ====
Thu 05/28 06Z 0.06 3514 82 88 6 0.00
Thu 05/28 07Z 0.08 3515 83 81 6 0.00
Thu 05/28 08Z 0.06 3516 83 78 6 0.00
Thu 05/28 09Z 0.07 3515 83 76 6 0.00
Thu 05/28 10Z 0.08 3515 83 73 6 0.00
Thu 05/28 11Z 0.12 3415 83 79 5 0.00
Thu 05/28 12Z 0.16 3416 87 86 5 0.00
Thu 05/28 13Z 0.16 3415 89 88 4 0.00
Thu 05/28 14Z 0.17 3417 90 89 4 0.00
Thu 05/28 15Z 0.20 3419 88 83 3 0.01
Thu 05/28 16Z 0.30 3420 86 73 3 0.01
Thu 05/28 17Z 1.20 3419 90 65 3 0.01
Thu 05/28 18Z 0.99 3419 91 60 3 0.01
Thu 05/28 19Z 1.07 3319 92 67 4 0.02
Thu 05/28 20Z 0.79 3420 91 64 4 0.02
Thu 05/28 21Z 0.65 3421 90 62 4 0.01
Thu 05/28 22Z 0.48 3421 92 61 4 0.01
Thu 05/28 23Z 0.37 3423 93 56 3 0.01
Fri 05/29 00Z 0.30 3424 92 48 3 0.00
Fri 05/29 01Z 0.34 3424 93 46 3 0.00
Fri 05/29 02Z 0.31 3424 93 45 3 0.00
Fri 05/29 03Z 0.33 3424 94 40 3 0.01
Fri 05/29 04Z 0.32 3423 96 38 3 0.01
Fri 05/29 05Z 0.34 3322 97 41 3 0.01
Fri 05/29 06Z 0.37 3322 98 50 3 0.02
Fri 05/29 07Z 0.39 3322 96 74 2 0.01
Fri 05/29 08Z 0.51 3323 91 84 2 0.00
Fri 05/29 09Z 0.57 3224 84 85 1 0.00
Fri 05/29 10Z 0.57 3225 77 83 1 0.00
Fri 05/29 11Z 0.54 3224 81 81 1 0.00
Fri 05/29 12Z 0.50 3221 81 78 1 0.00
Fri 05/29 13Z 0.46 3219 79 68 2 0.00
Fri 05/29 14Z 0.52 3216 74 59 2 0.00
Fri 05/29 15Z 1.50 3012 70 56 3 0.00
Fri 05/29 16Z 3.53 2710 70 67 3 0.00
Fri 05/29 17Z 5.70 2412 71 77 4 0.00
Fri 05/29 18Z 7.94 2416 67 92 5 0.00
Fri 05/29 19Z 10.32 2418 63 96 6 0.00
Fri 05/29 20Z 4.31 2522 75 95 5 0.03
Fri 05/29 21Z 1.23 2523 86 95 4 0.06
Fri 05/29 22Z 1.06 2523 92 97 3 0.09
Fri 05/29 23Z 0.73 2520 97 96 4 0.13
Sat 05/30 00Z 0.66 2518 97 85 4 0.10
Sat 05/30 01Z 0.73 2717 97 86 3 0.12
Sat 05/30 02Z 0.68 3022 90 81 1 0.07
Sat 05/30 03Z 0.49 3121 82 69 1 0.01
Sat 05/30 04Z 0.44 3118 91 79 0 0.01
Sat 05/30 05Z 0.37 3317 95 79 0 0.03
Sat 05/30 06Z 0.37 0016 95 83 0 0.07
Sat 05/30 07Z 0.51 0321 97 88 0 0.08
Sat 05/30 08Z 0.82 0528 98 88 0 0.07
Sat 05/30 09Z 1.10 0633 97 85 0 0.05
Sat 05/30 10Z 0.88 0532 93 91 0 0.06
Sat 05/30 11Z 0.68 0429 85 88 0 0.03
Sat 05/30 12Z 0.57 0426 80 79 0 0.01
Sat 05/30 13Z 0.59 0422 83 76 -1 0.00
Sat 05/30 14Z 1.36 0319 90 69 -2 0.00
Sat 05/30 15Z 1.90 0217 90 67 -2 0.00
Sat 05/30 16Z 2.85 0216 88 64 -2 0.00
Sat 05/30 17Z 2.84 0116 85 66 -1 0.00
Run total areal avg QPF for the greens is: 1.19 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