Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260722_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)
=== ===== === ==== ==== === === === ====
Wed 07/22 06Z 0.26 2019 97 87 14 0.00
Wed 07/22 07Z 0.25 2022 98 92 14 0.02
Wed 07/22 08Z 0.44 2124 98 86 14 0.16
Wed 07/22 09Z 0.72 2325 99 82 14 0.19
Wed 07/22 10Z 0.69 2520 97 68 14 0.08
Wed 07/22 11Z 0.55 2615 97 65 13 0.01
Wed 07/22 12Z 0.52 2514 97 80 13 0.01
Wed 07/22 13Z 0.53 2514 95 87 13 0.01
Wed 07/22 14Z 0.62 2516 96 95 13 0.06
Wed 07/22 15Z 0.61 2517 88 89 13 0.03
Wed 07/22 16Z 1.48 2420 90 74 12 0.00
Wed 07/22 17Z 1.90 2422 94 51 12 0.06
Wed 07/22 18Z 1.11 2525 90 31 11 0.07
Wed 07/22 19Z 2.32 2525 91 36 11 0.02
Wed 07/22 20Z 4.13 2524 89 48 10 0.01
Wed 07/22 21Z 5.62 2524 87 51 9 0.01
Wed 07/22 22Z 5.59 2625 86 47 9 0.00
Wed 07/22 23Z 1.87 2625 89 43 8 0.00
Thu 07/23 00Z 1.59 2725 91 38 8 0.00
Thu 07/23 01Z 1.26 2725 94 33 7 0.01
Thu 07/23 02Z 1.18 2825 94 32 6 0.01
Thu 07/23 03Z 0.99 2924 94 34 6 0.00
Thu 07/23 04Z 0.87 2924 94 31 5 0.00
Thu 07/23 05Z 0.70 3025 90 28 6 0.00
Thu 07/23 06Z 0.62 3126 85 28 6 0.00
Thu 07/23 07Z 0.55 3125 81 33 6 0.00
Thu 07/23 08Z 0.47 3224 72 41 6 0.00
Thu 07/23 09Z 0.39 3222 61 40 6 0.00
Thu 07/23 10Z 0.36 3220 56 35 6 0.00
Thu 07/23 11Z 0.40 3117 54 29 6 0.00
Thu 07/23 12Z 0.50 3016 57 23 6 0.00
Thu 07/23 13Z 0.71 2916 68 18 6 0.00
Thu 07/23 14Z 1.15 2817 74 21 6 0.00
Thu 07/23 15Z 2.50 2716 72 28 6 0.00
Thu 07/23 16Z 5.66 2615 77 28 6 0.00
Thu 07/23 17Z 7.51 2614 80 22 7 0.00
Thu 07/23 18Z 6.95 2614 79 21 7 0.00
Thu 07/23 19Z 5.72 2613 78 17 8 0.00
Thu 07/23 20Z 4.66 2611 77 14 8 0.00
Thu 07/23 21Z 3.65 2611 77 21 9 0.00
Thu 07/23 22Z 2.05 2511 77 25 9 0.00
Thu 07/23 23Z 1.12 2511 77 28 9 0.00
Fri 07/24 00Z 0.85 2511 75 24 9 0.00
Fri 07/24 01Z 0.75 2511 74 21 9 0.00
Fri 07/24 02Z 0.78 2511 73 17 9 0.00
Fri 07/24 03Z 0.80 2511 74 14 9 0.00
Fri 07/24 04Z 0.66 2510 72 12 9 0.00
Fri 07/24 05Z 0.52 2510 70 13 9 0.00
Fri 07/24 06Z 0.43 2510 66 16 9 0.00
Fri 07/24 07Z 0.44 2510 65 16 9 0.00
Fri 07/24 08Z 0.42 2509 65 16 9 0.00
Fri 07/24 09Z 0.39 2508 63 17 9 0.00
Fri 07/24 10Z 0.30 2407 60 18 9 0.00
Fri 07/24 11Z 0.26 2306 57 19 9 0.00
Fri 07/24 12Z 0.24 2306 54 21 9 0.00
Fri 07/24 13Z 0.23 2406 51 21 9 0.00
Fri 07/24 14Z 0.21 2304 49 19 10 0.00
Fri 07/24 15Z 0.43 2304 52 17 10 0.00
Fri 07/24 16Z 0.51 2203 52 16 10 0.00
Fri 07/24 17Z 0.58 2103 51 16 10 0.00
Run total areal avg QPF for the greens is: 0.76 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