NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260914_1800
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)
=== ===== === ==== ==== === === === ====
Mon 09/14 18Z 4.39 3215  84  14   4 0.00
Mon 09/14 19Z 3.46 3217  83  18   4 0.00
Mon 09/14 20Z 1.99 3218  81  19   4 0.00
Mon 09/14 21Z 1.61 3218  82  18   4 0.00
Mon 09/14 22Z 0.87 3219  82  17   4 0.00
Mon 09/14 23Z 0.75 3221  80  16   4 0.00
Tue 09/15 00Z 0.55 3320  81  13   4 0.00
Tue 09/15 01Z 0.52 3321  83  12   4 0.00
Tue 09/15 02Z 0.39 3321  83  10   4 0.00
Tue 09/15 03Z 0.14 3419  81   9   4 0.00
Tue 09/15 04Z 0.04 3418  75   8   5 0.00
Tue 09/15 05Z 0.05 3513  66   7   7 0.00
Tue 09/15 06Z 0.05 3510  64   7   7 0.00
Tue 09/15 07Z 0.05 0008  62   7   7 0.00
Tue 09/15 08Z 0.05 3308  64   7   6 0.00
Tue 09/15 09Z 0.01 3408  62   6   6 0.00
Tue 09/15 10Z 0.04 0005  59   8   7 0.00
Tue 09/15 11Z 0.06 0602  56  10   7 0.00
Tue 09/15 12Z 0.05 1303  54  13   7 0.00
Tue 09/15 13Z 0.04 1704  55  14   7 0.00
Tue 09/15 14Z 0.05 1904  57  16   7 0.00
Tue 09/15 15Z 0.07 2004  58  17   8 0.00
Tue 09/15 16Z 0.06 1906  58  17   8 0.00
Tue 09/15 17Z 0.13 2008  59  16   9 0.00
Tue 09/15 18Z 0.16 1909  58  15   9 0.00
Tue 09/15 19Z 0.16 1910  59  13   9 0.00
Tue 09/15 20Z 0.25 2010  61  11   9 0.00
Tue 09/15 21Z 0.16 2013  49  17  12 0.00
Tue 09/15 22Z 0.18 2015  44  34  13 0.00
Tue 09/15 23Z 0.22 2017  42  72  14 0.00
Wed 09/16 00Z 0.25 2019  39  89  14 0.00
Wed 09/16 01Z 0.27 2120  34  88  15 0.00
Wed 09/16 02Z 0.26 2121  31  83  15 0.00
Wed 09/16 03Z 0.33 2121  35  86  15 0.00
Wed 09/16 04Z 0.36 2222  41  91  15 0.00
Wed 09/16 05Z 0.39 2322  45  88  15 0.00
Wed 09/16 06Z 0.40 2321  45  89  15 0.00
Wed 09/16 07Z 0.43 2423  46  90  15 0.00
Wed 09/16 08Z 0.48 2424  52  91  15 0.00
Wed 09/16 09Z 0.46 2423  53  90  15 0.00
Wed 09/16 10Z 0.47 2523  59  93  15 0.00
Wed 09/16 11Z 0.46 2522  62  92  15 0.00
Wed 09/16 12Z 0.45 2522  72  94  15 0.00
Wed 09/16 13Z 0.50 2523  77  90  15 0.01
Wed 09/16 14Z 0.52 2523  85  89  15 0.02
Wed 09/16 15Z 0.53 2622  92  79  15 0.00
Wed 09/16 16Z 0.49 2721  95  83  15 0.01
Wed 09/16 17Z 0.43 2819  97  88  15 0.02
Wed 09/16 18Z 0.35 2816  98  77  15 0.01
Wed 09/16 19Z 0.29 2913  98  81  14 0.01
Wed 09/16 20Z 0.22 2911  98  71  14 0.00
Wed 09/16 21Z 0.18 3009  99  78  14 0.01
Wed 09/16 22Z 0.16 3008  98  70  13 0.00
Wed 09/16 23Z 0.15 3008  97  41  13 0.00
Thu 09/17 00Z 0.13 3107  95  19  13 0.00
Thu 09/17 01Z 0.12 3106  94  17  12 0.00
Thu 09/17 02Z 0.10 3005  94  14  12 0.00
Thu 09/17 03Z 0.09 2904  94  13  12 0.00
Thu 09/17 04Z 0.09 2803  94  15  12 0.00
Thu 09/17 05Z 0.09 2703  94  12  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.09 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