NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260908_0600
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 09/08 06Z 0.34 3316  80  53  10 0.00
Tue 09/08 07Z 0.39 3217  81  56  10 0.00
Tue 09/08 08Z 0.39 3216  82  62  10 0.00
Tue 09/08 09Z 0.44 3116  82  66  10 0.00
Tue 09/08 10Z 0.50 3016  82  71  10 0.00
Tue 09/08 11Z 0.58 2917  84  74  10 0.00
Tue 09/08 12Z 0.56 3017  87  77   9 0.01
Tue 09/08 13Z 0.51 3016  90  84   9 0.04
Tue 09/08 14Z 0.40 3115  90  83   9 0.01
Tue 09/08 15Z 0.33 3113  89  68   9 0.00
Tue 09/08 16Z 0.32 3112  89  63   9 0.00
Tue 09/08 17Z 0.32 3112  90  64   9 0.01
Tue 09/08 18Z 0.28 3211  90  53   9 0.00
Tue 09/08 19Z 0.23 3210  90  48  10 0.00
Tue 09/08 20Z 0.20 3210  88  39  10 0.00
Tue 09/08 21Z 0.13 3208  84  30  10 0.00
Tue 09/08 22Z 0.15 3207  81  23  10 0.00
Tue 09/08 23Z 0.12 3206  77  30  11 0.00
Wed 09/09 00Z 0.09 3104  72  23  11 0.00
Wed 09/09 01Z 0.08 3003  69  14  11 0.00
Wed 09/09 02Z 0.08 2602  69   6  11 0.00
Wed 09/09 03Z 0.09 2303  70   5  11 0.00
Wed 09/09 04Z 0.09 2205  72   5  11 0.00
Wed 09/09 05Z 0.13 2207  76   4  11 0.00
Wed 09/09 06Z 0.15 2108  81   5  11 0.00
Wed 09/09 07Z 0.18 2111  87   7  11 0.01
Wed 09/09 08Z 0.23 2113  90  17  11 0.01
Wed 09/09 09Z 0.22 2213  88  57  12 0.01
Wed 09/09 10Z 0.24 2213  88  63  12 0.01
Wed 09/09 11Z 0.34 2315  93  55  11 0.01
Wed 09/09 12Z 0.33 2314  91  61  11 0.01
Wed 09/09 13Z 0.36 2216  92  65  11 0.00
Wed 09/09 14Z 0.42 2220  90  66  12 0.00
Wed 09/09 15Z 0.35 2119  81  59  13 0.00
Wed 09/09 16Z 0.44 2222  77  52  12 0.00
Wed 09/09 17Z 0.45 2122  80  58  12 0.01
Wed 09/09 18Z 0.37 2023  82  55  12 0.01
Wed 09/09 19Z 0.42 2126  94  67  12 0.01
Wed 09/09 20Z 0.46 2127  92  90  13 0.05
Wed 09/09 21Z 0.45 2030  94  91  13 0.06
Wed 09/09 22Z 0.49 2035  97  92  14 0.08
Wed 09/09 23Z 0.65 2138  97  91  14 0.06
Thu 09/10 00Z 0.76 2238  97  91  15 0.03
Thu 09/10 01Z 0.86 2239  97  86  15 0.03
Thu 09/10 02Z 0.91 2339  97  81  15 0.04
Thu 09/10 03Z 0.94 2338  96  74  15 0.06
Thu 09/10 04Z 0.95 2339  96  73  15 0.03
Thu 09/10 05Z 0.95 2338  97  80  15 0.06
Thu 09/10 06Z 0.97 2338  97  87  15 0.09
Thu 09/10 07Z 0.95 2437  98  92  15 0.14
Thu 09/10 08Z 0.99 2534  97  81  15 0.12
Thu 09/10 09Z 0.98 2632  94  49  14 0.07
Thu 09/10 10Z 1.00 2729  89  38  14 0.03
Thu 09/10 11Z 1.03 2728  86  28  13 0.02
Thu 09/10 12Z 1.13 2729  87  29  12 0.01
Thu 09/10 13Z 1.23 2729  88  27  11 0.01
Thu 09/10 14Z 1.21 2728  87  25  11 0.01
Thu 09/10 15Z 1.49 2726  84  22  10 0.01
Thu 09/10 16Z 4.46 2724  81  14   9 0.00
Thu 09/10 17Z 9.79 2723  77  11   9 0.00

Run total areal avg QPF for the greens is: 1.17 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