Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260415_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)
=== ===== === ==== ==== === === === ====
Wed 04/15 12Z 0.13 2807 64 27 13 0.00
Wed 04/15 13Z 0.16 2708 54 25 13 0.00
Wed 04/15 14Z 0.17 2508 53 24 13 0.00
Wed 04/15 15Z 0.23 2411 58 18 13 0.00
Wed 04/15 16Z 0.25 2212 50 68 12 0.00
Wed 04/15 17Z 0.28 2211 47 98 11 0.00
Wed 04/15 18Z 0.31 2212 66 95 10 0.01
Wed 04/15 19Z 0.41 2215 77 84 11 0.00
Wed 04/15 20Z 0.77 2217 84 79 11 0.00
Wed 04/15 21Z 0.69 2315 85 66 11 0.00
Wed 04/15 22Z 0.73 2316 90 53 11 0.00
Wed 04/15 23Z 0.69 2318 92 45 11 0.00
Thu 04/16 00Z 0.82 2521 94 57 11 0.00
Thu 04/16 01Z 0.84 2622 91 57 11 0.00
Thu 04/16 02Z 0.62 2618 88 73 11 0.00
Thu 04/16 03Z 0.58 2618 87 84 11 0.00
Thu 04/16 04Z 0.45 2615 81 83 12 0.00
Thu 04/16 05Z 0.24 2809 76 88 12 0.00
Thu 04/16 06Z 0.26 2508 91 93 10 0.09
Thu 04/16 07Z 0.13 2105 94 97 10 0.06
Thu 04/16 08Z 0.07 1905 93 95 11 0.03
Thu 04/16 09Z 0.07 1906 92 96 12 0.01
Thu 04/16 10Z 0.12 2105 92 92 12 0.04
Thu 04/16 11Z 0.21 2707 94 79 11 0.01
Thu 04/16 12Z 0.24 2810 91 55 11 0.00
Thu 04/16 13Z 0.32 2913 91 33 10 0.00
Thu 04/16 14Z 0.31 2913 89 27 11 0.00
Thu 04/16 15Z 0.25 2911 86 42 11 0.00
Thu 04/16 16Z 0.28 2709 84 68 11 0.00
Thu 04/16 17Z 0.36 2609 83 77 11 0.00
Thu 04/16 18Z 0.41 2309 79 82 12 0.00
Thu 04/16 19Z 0.48 2211 75 77 12 0.00
Thu 04/16 20Z 0.56 2115 75 43 13 0.00
Thu 04/16 21Z 0.71 2117 76 29 13 0.00
Thu 04/16 22Z 0.63 2120 83 22 13 0.00
Thu 04/16 23Z 0.59 2021 86 20 13 0.00
Fri 04/17 00Z 0.51 2018 89 73 13 0.02
Fri 04/17 01Z 0.75 2620 95 91 12 0.56
Fri 04/17 02Z 0.72 2822 88 92 11 0.12
Fri 04/17 03Z 0.72 2720 92 90 10 0.01
Fri 04/17 04Z 0.72 2719 89 85 10 0.01
Fri 04/17 05Z 0.73 2721 91 69 10 0.02
Fri 04/17 06Z 0.65 2721 87 65 10 0.01
Fri 04/17 07Z 0.67 2620 90 72 9 0.01
Fri 04/17 08Z 0.67 2720 97 70 9 0.04
Fri 04/17 09Z 0.59 2820 96 69 9 0.05
Fri 04/17 10Z 0.45 2920 95 75 9 0.03
Fri 04/17 11Z 0.30 3118 96 80 8 0.02
Fri 04/17 12Z 0.18 3318 95 80 8 0.01
Fri 04/17 13Z 0.13 3520 95 79 7 0.00
Fri 04/17 14Z 0.13 0020 95 78 7 0.00
Fri 04/17 15Z 0.19 0020 94 78 6 0.00
Fri 04/17 16Z 0.24 0118 93 78 7 0.00
Fri 04/17 17Z 0.24 0117 92 75 7 0.00
Fri 04/17 18Z 0.27 0115 89 70 7 0.00
Fri 04/17 19Z 0.42 0113 87 61 7 0.00
Fri 04/17 20Z 0.40 0211 86 51 7 0.00
Fri 04/17 21Z 0.43 0210 85 37 7 0.00
Fri 04/17 22Z 0.28 0309 85 23 7 0.00
Fri 04/17 23Z 0.22 0309 83 19 8 0.00
Run total areal avg QPF for the Central_Greens is: 1.16 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