Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260210_1800
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)
=== ===== === ==== ==== === === === ====
Tue 02/10 18Z 0.12 2109  55  68  -5 0.00
Tue 02/10 19Z 0.07 1910  48  85  -4 0.00
Tue 02/10 20Z 0.05 1814  47  97  -5 0.00
Tue 02/10 21Z 0.04 1818  64  95  -6 0.00
Tue 02/10 23Z 0.04 1825  95  97  -4 0.05
Wed 02/11 00Z 0.15 1926  95  96  -4 0.07
Wed 02/11 01Z 0.26 2025  95  95  -5 0.08
Wed 02/11 02Z 0.31 2124  96  95  -5 0.08
Wed 02/11 03Z 0.37 2223  97  95  -4 0.07
Wed 02/11 04Z 0.41 2321  97  94  -4 0.05
Wed 02/11 05Z 0.45 2520  97  68  -5 0.05
Wed 02/11 06Z 0.48 2619  97  37  -6 0.03
Wed 02/11 07Z 0.47 2718  97  21  -6 0.02
Wed 02/11 08Z 0.48 2718  96  17  -6 0.01
Wed 02/11 09Z 0.51 2819  97  20  -7 0.01
Wed 02/11 11Z 0.49 2819  97  45  -7 0.01
Wed 02/11 12Z 0.49 2919  96  55  -8 0.01
Wed 02/11 13Z 0.50 2919  96  65  -8 0.01
Wed 02/11 14Z 0.55 2819  97  76  -9 0.01
Wed 02/11 15Z 0.63 2818  97  81  -9 0.01
Wed 02/11 16Z 0.75 2818  96  84  -9 0.01
Wed 02/11 17Z 0.95 2817  96  86  -9 0.01
Wed 02/11 18Z 1.19 2817  96  85  -9 0.01
Wed 02/11 19Z 1.18 2918  96  85 -10 0.01
Wed 02/11 20Z 1.06 2919  96  85 -10 0.01
Wed 02/11 21Z 0.90 3019  96  85 -10 0.02
Wed 02/11 22Z 0.93 3020  95  84 -11 0.02
Wed 02/11 23Z 0.84 3121  95  83 -11 0.02
Thu 02/12 00Z 0.68 3222  96  82 -12 0.02
Thu 02/12 01Z 0.51 3223  96  83 -12 0.02
Thu 02/12 02Z 0.41 3324  96  83 -12 0.01
Thu 02/12 03Z 0.37 3323  96  84 -12 0.01
Thu 02/12 04Z 0.35 3323  95  84 -11 0.01
Thu 02/12 05Z 0.29 3323  94  82 -11 0.01
Thu 02/12 06Z 0.25 3423  94  79 -11 0.01
Thu 02/12 07Z 0.21 3424  94  78 -11 0.01
Thu 02/12 09Z 0.17 3422  94  78 -11 0.01
Thu 02/12 10Z 0.17 3423  94  78 -11 0.01
Thu 02/12 11Z 0.16 3424  94  75 -12 0.01
Thu 02/12 12Z 0.17 3424  94  74 -12 0.01
Thu 02/12 13Z 0.20 3423  94  71 -12 0.01
Thu 02/12 14Z 0.19 3423  93  69 -12 0.01
Thu 02/12 15Z 0.18 3423  93  68 -12 0.01
Thu 02/12 16Z 0.18 3422  93  67 -11 0.01
Thu 02/12 17Z 0.18 3423  92  64 -11 0.01
Thu 02/12 18Z 0.19 3323  92  61 -11 0.00
Thu 02/12 19Z 0.20 3323  91  52 -11 0.00
Thu 02/12 20Z 0.22 3323  90  35 -11 0.00
Thu 02/12 21Z 0.24 3324  86  24 -11 0.00
Thu 02/12 22Z 0.21 3324  75  15 -11 0.00
Thu 02/12 23Z 0.16 3425  67  10 -10 0.00
Fri 02/13 00Z 0.13 3425  64  13 -10 0.00
Fri 02/13 01Z 0.13 3425  66  15 -10 0.00
Fri 02/13 02Z 0.13 3425  69  16 -10 0.00
Fri 02/13 04Z 0.11 3423  67  16  -9 0.00
Fri 02/13 05Z 0.10 3422  65  16  -9 0.00

Run total areal avg QPF for the greens is: 0.87 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