NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260914_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)
=== ===== === ==== ==== === === === ====
Mon 09/14 18Z 4.49 3215  86  18   3 0.00
Mon 09/14 19Z 3.98 3217  85  21   4 0.00
Mon 09/14 20Z 2.58 3217  83  22   4 0.00
Mon 09/14 21Z 2.02 3218  85  22   4 0.00
Mon 09/14 22Z 1.36 3219  83  21   4 0.00
Mon 09/14 23Z 1.28 3221  82  19   4 0.00
Tue 09/15 00Z 1.11 3220  82  17   3 0.00
Tue 09/15 01Z 0.90 3220  83  16   3 0.00
Tue 09/15 02Z 0.70 3320  83  12   3 0.00
Tue 09/15 03Z 0.31 3318  80  10   4 0.00
Tue 09/15 04Z 0.17 3416  75   9   5 0.00
Tue 09/15 05Z 0.05 3512  66   7   6 0.00
Tue 09/15 06Z 0.04 3509  65   7   6 0.00
Tue 09/15 07Z 0.03 3507  61   7   7 0.00
Tue 09/15 08Z 0.11 3208  64   7   6 0.00
Tue 09/15 09Z 0.06 3407  62   8   6 0.00
Tue 09/15 10Z 0.02 0004  58  10   6 0.00
Tue 09/15 11Z 0.04 0701  54  13   7 0.00
Tue 09/15 12Z 0.05 1503  51  15   7 0.00
Tue 09/15 13Z 0.05 1904  52  16   7 0.00
Tue 09/15 14Z 0.05 2005  54  17   7 0.00
Tue 09/15 15Z 0.06 2005  55  17   8 0.00
Tue 09/15 16Z 0.06 1907  56  17   8 0.00
Tue 09/15 17Z 0.09 2008  57  16   9 0.00
Tue 09/15 18Z 0.12 2010  57  15   9 0.00
Tue 09/15 19Z 0.13 2011  59  13   9 0.00
Tue 09/15 20Z 0.20 2012  59  13   9 0.00
Tue 09/15 21Z 0.12 1914  48  32  12 0.00
Tue 09/15 22Z 0.12 1917  43  48  13 0.00
Tue 09/15 23Z 0.18 2019  41  80  13 0.00
Wed 09/16 00Z 0.22 2020  36  91  14 0.00
Wed 09/16 01Z 0.23 2122  33  90  14 0.00
Wed 09/16 02Z 0.23 2122  31  87  15 0.00
Wed 09/16 03Z 0.30 2222  36  89  15 0.00
Wed 09/16 04Z 0.35 2222  42  93  14 0.00
Wed 09/16 05Z 0.38 2322  45  90  14 0.00
Wed 09/16 06Z 0.39 2322  43  91  14 0.00
Wed 09/16 07Z 0.43 2423  45  91  14 0.00
Wed 09/16 08Z 0.47 2424  48  91  14 0.00
Wed 09/16 09Z 0.47 2422  54  87  14 0.00
Wed 09/16 10Z 0.49 2522  63  87  14 0.00
Wed 09/16 11Z 0.47 2521  71  89  14 0.00
Wed 09/16 12Z 0.46 2520  78  84  15 0.00
Wed 09/16 13Z 0.49 2522  82  80  14 0.01
Wed 09/16 14Z 0.50 2521  88  78  15 0.01
Wed 09/16 15Z 0.49 2620  94  74  14 0.01
Wed 09/16 16Z 0.47 2719  96  75  14 0.02
Wed 09/16 17Z 0.43 2818  98  79  14 0.02
Wed 09/16 18Z 0.36 2815  98  73  14 0.02
Wed 09/16 19Z 0.32 2913  98  76  14 0.01
Wed 09/16 20Z 0.28 2912  98  64  13 0.01
Wed 09/16 21Z 0.24 3010  97  74  13 0.01
Wed 09/16 22Z 0.21 3009  94  61  13 0.00
Wed 09/16 23Z 0.21 3009  93  35  13 0.00
Thu 09/17 00Z 0.16 3108  91  17  13 0.00
Thu 09/17 01Z 0.15 3107  88  15  12 0.00
Thu 09/17 02Z 0.12 3106  87  11  12 0.00
Thu 09/17 03Z 0.10 3104  90  10  12 0.00
Thu 09/17 04Z 0.10 3004  92  11  12 0.01
Thu 09/17 05Z 0.09 2803  92   9  12 0.01

Run total areal avg QPF for the greens is: 0.14 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