NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260324_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)
=== ===== === ==== ==== === === === ====
Tue 03/24 18Z 2.99 2506  77   6  -9 0.00
Tue 03/24 19Z 2.99 2308  70   5  -8 0.00
Tue 03/24 20Z 2.33 2210  64   5  -7 0.00
Tue 03/24 21Z 1.66 2213  61   9  -7 0.00
Tue 03/24 22Z 1.24 2318  61  13  -7 0.00
Tue 03/24 23Z 1.21 2422  63  14  -7 0.00
Wed 03/25 00Z 1.56 2426  69  17  -7 0.00
Wed 03/25 01Z 2.54 2528  70  59  -7 0.00
Wed 03/25 02Z 3.21 2628  63  86  -8 0.00
Wed 03/25 03Z 2.04 2728  79  86  -8 0.00
Wed 03/25 04Z 1.30 2729  87  85  -8 0.00
Wed 03/25 05Z 1.03 2829  90  21  -8 0.00
Wed 03/25 06Z 0.97 2828  89  13  -8 0.00
Wed 03/25 07Z 0.97 2827  88  10  -8 0.00
Wed 03/25 08Z 0.87 2925  90  12  -9 0.00
Wed 03/25 09Z 0.76 2922  90  13  -9 0.01
Wed 03/25 10Z 0.66 3021  87  13  -8 0.00
Wed 03/25 11Z 0.58 2919  85  15  -9 0.00
Wed 03/25 12Z 0.56 2918  85  19  -9 0.00
Wed 03/25 13Z 0.60 2917  85  16  -9 0.00
Wed 03/25 14Z 0.49 2815  81  10  -8 0.00
Wed 03/25 15Z 0.47 2814  79   7  -8 0.00
Wed 03/25 16Z 0.47 2713  78   5  -8 0.00
Wed 03/25 17Z 0.44 2713  74   4  -7 0.00
Wed 03/25 18Z 0.43 2713  67   3  -6 0.00
Wed 03/25 19Z 0.37 2711  56   7  -5 0.00
Wed 03/25 20Z 0.37 2609  49  11  -5 0.00
Wed 03/25 21Z 0.37 2408  45  13  -4 0.00
Wed 03/25 22Z 0.32 2209  43   8  -4 0.00
Wed 03/25 23Z 0.30 2012  42   8  -4 0.00
Thu 03/26 00Z 0.37 2016  38  10  -3 0.00
Thu 03/26 01Z 0.49 2020  54  68  -3 0.00
Thu 03/26 02Z 0.67 2024  68  91  -3 0.00
Thu 03/26 03Z 0.97 2128  74  94  -3 0.00
Thu 03/26 04Z 0.94 2228  86  90  -3 0.00
Thu 03/26 05Z 0.77 2128  83  83  -1 0.00
Thu 03/26 06Z 0.78 2131  85  76  -1 0.00
Thu 03/26 07Z 0.74 2232  85  61   0 0.00
Thu 03/26 08Z 0.67 2232  82  75   0 0.00
Thu 03/26 09Z 0.64 2232  78  92   1 0.00
Thu 03/26 10Z 0.59 2330  77  89   1 0.00
Thu 03/26 11Z 0.59 2330  76  91   2 0.00
Thu 03/26 12Z 0.57 2329  77  92   2 0.00
Thu 03/26 13Z 0.61 2331  80  89   2 0.00
Thu 03/26 14Z 0.66 2332  83  91   3 0.00
Thu 03/26 15Z 0.72 2334  85  93   3 0.00
Thu 03/26 16Z 0.77 2236  83  90   4 0.00
Thu 03/26 17Z 0.81 2337  82  91   5 0.00
Thu 03/26 18Z 0.85 2237  83  95   5 0.01
Thu 03/26 19Z 0.98 2239  86  92   5 0.01
Thu 03/26 20Z 1.09 2238  85  87   6 0.00
Thu 03/26 21Z 1.18 2238  84  82   7 0.00
Thu 03/26 22Z 1.11 2240  85  87   7 0.00
Thu 03/26 23Z 0.99 2243  89  95   8 0.01
Fri 03/27 00Z 0.96 2244  94  93   8 0.05
Fri 03/27 01Z 1.07 2246  96  91   7 0.09
Fri 03/27 02Z 1.08 2344  97  91   8 0.14
Fri 03/27 03Z 1.02 2438  97  95   7 0.22
Fri 03/27 04Z 0.94 2629  98  96   6 0.23
Fri 03/27 05Z 0.93 2827  98  97   4 0.17

Run total areal avg QPF for the Central_Greens is: 0.94 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