Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260805_1200
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)
=== ===== === ==== ==== === === === ====
Wed 08/05 12Z 0.23 2607 74 38 15 0.00
Wed 08/05 13Z 0.21 2606 74 37 15 0.00
Wed 08/05 14Z 0.16 2504 72 35 15 0.00
Wed 08/05 15Z 0.20 2304 71 33 15 0.00
Wed 08/05 16Z 0.28 2104 71 29 15 0.00
Wed 08/05 17Z 0.50 2106 71 23 15 0.00
Wed 08/05 18Z 0.76 2207 70 17 15 0.00
Wed 08/05 19Z 0.64 2207 67 12 16 0.00
Wed 08/05 20Z 0.64 2208 64 10 16 0.00
Wed 08/05 21Z 0.53 2208 63 11 16 0.00
Wed 08/05 22Z 0.51 2309 68 13 16 0.00
Wed 08/05 23Z 0.54 2310 75 16 15 0.00
Thu 08/06 00Z 0.51 2310 78 20 15 0.00
Thu 08/06 01Z 0.51 2311 80 26 15 0.00
Thu 08/06 02Z 0.51 2311 80 26 15 0.00
Thu 08/06 03Z 0.50 2312 81 22 15 0.00
Thu 08/06 04Z 0.45 2313 83 23 16 0.00
Thu 08/06 05Z 0.45 2314 84 25 16 0.00
Thu 08/06 06Z 0.47 2315 86 38 16 0.00
Thu 08/06 07Z 0.44 2415 85 50 16 0.01
Thu 08/06 08Z 0.39 2413 83 52 16 0.01
Thu 08/06 09Z 0.35 2411 82 49 16 0.00
Thu 08/06 10Z 0.30 2410 83 46 16 0.00
Thu 08/06 11Z 0.23 2309 83 47 16 0.00
Thu 08/06 12Z 0.19 2208 83 59 16 0.00
Thu 08/06 13Z 0.17 2207 85 70 16 0.00
Thu 08/06 14Z 0.20 2207 88 82 16 0.00
Thu 08/06 15Z 0.24 2207 90 78 16 0.00
Thu 08/06 16Z 0.28 2206 91 71 16 0.00
Thu 08/06 17Z 0.38 2206 90 76 16 0.00
Thu 08/06 18Z 0.42 2207 89 72 16 0.00
Thu 08/06 19Z 0.44 2206 88 72 17 0.00
Thu 08/06 20Z 0.39 2206 87 72 17 0.00
Thu 08/06 21Z 0.35 2207 87 75 17 0.01
Thu 08/06 22Z 0.24 2207 88 74 17 0.04
Thu 08/06 23Z 0.32 2309 87 77 17 0.08
Fri 08/07 00Z 0.37 2310 90 73 17 0.11
Fri 08/07 01Z 0.42 2411 86 61 17 0.10
Fri 08/07 02Z 0.49 2613 86 42 17 0.02
Fri 08/07 03Z 0.48 2715 89 49 17 0.01
Fri 08/07 04Z 0.49 2716 85 51 17 0.02
Fri 08/07 05Z 0.46 2716 78 60 17 0.00
Fri 08/07 06Z 0.45 2716 72 67 17 0.00
Fri 08/07 07Z 0.44 2716 68 65 17 0.00
Fri 08/07 08Z 0.42 2816 72 66 17 0.00
Fri 08/07 09Z 0.37 2914 73 59 17 0.00
Fri 08/07 10Z 0.34 3014 78 63 16 0.00
Fri 08/07 11Z 0.31 3013 81 65 16 0.00
Fri 08/07 12Z 0.30 3013 83 71 16 0.00
Fri 08/07 13Z 0.27 3112 84 72 16 0.00
Fri 08/07 14Z 0.24 3110 84 69 16 0.00
Fri 08/07 15Z 0.22 3109 83 70 16 0.00
Fri 08/07 16Z 0.21 3007 85 70 16 0.00
Fri 08/07 17Z 0.26 2905 85 72 16 0.00
Fri 08/07 18Z 0.38 2805 85 73 16 0.00
Fri 08/07 19Z 0.53 2705 85 73 16 0.00
Fri 08/07 20Z 0.43 2605 84 73 16 0.00
Fri 08/07 21Z 0.31 2605 83 71 17 0.00
Fri 08/07 22Z 0.29 2506 84 71 17 0.00
Fri 08/07 23Z 0.28 2407 84 71 17 0.00
Run total areal avg QPF for the greens is: 0.41 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