NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260421_0600
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)
=== ===== === ==== ==== === === === ====
Tue 04/21 06Z 0.26 3107  71  23  -9 0.00
Tue 04/21 07Z 0.48 2906  67  23  -9 0.00
Tue 04/21 08Z 0.53 2705  70  25  -9 0.00
Tue 04/21 09Z 0.51 2506  73  23  -9 0.00
Tue 04/21 10Z 0.50 2507  76  19  -9 0.00
Tue 04/21 11Z 0.42 2407  77  13  -9 0.00
Tue 04/21 12Z 0.41 2307  78  11  -9 0.00
Tue 04/21 13Z 1.09 2308  77  10  -9 0.00
Tue 04/21 14Z 2.63 2407  75   9  -9 0.00
Tue 04/21 15Z 4.42 2407  71   9  -8 0.00
Tue 04/21 16Z 4.39 2406  65   8  -7 0.00
Tue 04/21 17Z 4.40 2307  60  12  -7 0.00
Tue 04/21 18Z 4.32 2207  57  24  -6 0.00
Tue 04/21 19Z 4.39 2208  54  59  -5 0.00
Tue 04/21 20Z 3.72 2208  52  85  -5 0.00
Tue 04/21 21Z 2.87 2208  50  86  -4 0.00
Tue 04/21 22Z 1.36 2210  47  79  -4 0.00
Tue 04/21 23Z 0.51 2210  43  72  -4 0.00
Wed 04/22 00Z 0.46 2111  42  73  -4 0.00
Wed 04/22 01Z 0.56 2113  50  79  -4 0.00
Wed 04/22 02Z 0.59 2116  53  78  -4 0.00
Wed 04/22 03Z 0.55 2118  50  77  -3 0.00
Wed 04/22 04Z 0.59 2219  51  81  -3 0.00
Wed 04/22 05Z 0.62 2221  54  79  -3 0.00
Wed 04/22 06Z 0.60 2222  66  77  -3 0.00
Wed 04/22 07Z 0.46 2219  74  83  -2 0.00
Wed 04/22 08Z 0.31 2215  71  91  -1 0.00
Wed 04/22 09Z 0.24 2113  74  89  -1 0.00
Wed 04/22 10Z 0.24 2114  88  91  -1 0.00
Wed 04/22 11Z 0.25 2017  96  89  -1 0.00
Wed 04/22 12Z 0.25 1919  97  75  -1 0.01
Wed 04/22 13Z 0.24 2018  96  54  -1 0.00
Wed 04/22 14Z 0.26 2016  97  49  -1 0.00
Wed 04/22 15Z 0.25 2015  97  35  -2 0.01
Wed 04/22 16Z 0.24 2013  97  25  -2 0.01
Wed 04/22 17Z 0.26 2013  97  14  -1 0.01
Wed 04/22 18Z 0.27 2112  97  10  -1 0.01
Wed 04/22 19Z 0.28 2111  97   8  -1 0.01
Wed 04/22 20Z 0.26 2210  98   6  -1 0.01
Wed 04/22 21Z 0.23 2209  98   5   0 0.01
Wed 04/22 22Z 0.22 2408  98   6   0 0.00
Wed 04/22 23Z 0.21 2507  98   7   0 0.01
Thu 04/23 00Z 0.20 2707  97   9   0 0.00
Thu 04/23 01Z 0.20 2807  96   8   0 0.00
Thu 04/23 02Z 0.22 2808  96  11   0 0.00
Thu 04/23 03Z 0.24 2809  96  18   0 0.00
Thu 04/23 04Z 0.28 2810  96  34   0 0.01
Thu 04/23 05Z 0.32 2811  96  35  -1 0.01
Thu 04/23 06Z 0.33 2811  95  69  -1 0.01
Thu 04/23 07Z 0.38 2913  94  83  -1 0.01
Thu 04/23 08Z 0.36 2914  91  85  -1 0.01
Thu 04/23 09Z 0.36 3015  90  84   0 0.01
Thu 04/23 10Z 0.39 3017  91  85  -1 0.01
Thu 04/23 11Z 0.46 3020  95  86  -1 0.02
Thu 04/23 12Z 0.53 3124  97  90  -1 0.03
Thu 04/23 13Z 0.44 3224  98  79  -2 0.03
Thu 04/23 14Z 0.41 3224  98  43  -3 0.02
Thu 04/23 15Z 0.43 3324  97  25  -3 0.02
Thu 04/23 16Z 1.25 3223  94  23  -4 0.01
Thu 04/23 17Z 2.42 3223  89  24  -4 0.00

Run total areal avg QPF for the Central_Greens is: 0.29 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