NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260325_0000
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)
=== ===== === ==== ==== === === === ====
Wed 03/25 00Z 1.10 2520  63  51  -7 0.00
Wed 03/25 01Z 2.79 2625  65  77  -8 0.00
Wed 03/25 02Z 4.86 2727  67  89  -9 0.00
Wed 03/25 03Z 3.25 2727  75  81  -9 0.00
Wed 03/25 04Z 1.69 2827  82  47  -9 0.00
Wed 03/25 05Z 1.20 2826  85  23  -9 0.00
Wed 03/25 06Z 1.02 2826  86  32  -9 0.00
Wed 03/25 07Z 1.02 2828  91  36  -9 0.00
Wed 03/25 08Z 1.05 2829  93  20  -9 0.01
Wed 03/25 09Z 1.05 2928  92  14  -9 0.01
Wed 03/25 10Z 0.96 2924  90  15  -9 0.01
Wed 03/25 11Z 0.87 2922  89  20  -9 0.01
Wed 03/25 12Z 0.72 2920  90  27  -9 0.01
Wed 03/25 13Z 0.65 2920  88  34  -9 0.01
Wed 03/25 14Z 0.55 2918  84  34  -9 0.01
Wed 03/25 15Z 0.46 2815  80  29  -9 0.00
Wed 03/25 16Z 0.45 2713  76  21  -8 0.00
Wed 03/25 17Z 0.45 2613  72  15  -7 0.00
Wed 03/25 18Z 0.43 2512  63  11  -6 0.00
Wed 03/25 19Z 0.47 2511  54   9  -5 0.00
Wed 03/25 20Z 0.44 2310  47   8  -5 0.00
Wed 03/25 21Z 0.35 2210  44   6  -4 0.00
Wed 03/25 22Z 0.24 2012  43   6  -4 0.00
Wed 03/25 23Z 0.24 1916  46  55  -3 0.00
Thu 03/26 00Z 0.32 1921  55  82  -3 0.00
Thu 03/26 01Z 0.50 2026  62  87  -3 0.00
Thu 03/26 02Z 0.78 2029  72  90  -3 0.00
Thu 03/26 03Z 0.77 2132  89  92  -3 0.01
Thu 03/26 04Z 0.70 2232  92  94  -2 0.01
Thu 03/26 05Z 0.72 2135  84  94  -2 0.00
Thu 03/26 06Z 0.66 2233  81  90  -1 0.00
Thu 03/26 07Z 0.56 2231  74  92   0 0.00
Thu 03/26 08Z 0.64 2233  81  95   0 0.00
Thu 03/26 09Z 0.60 2331  83  96   0 0.02
Thu 03/26 10Z 0.63 2333  84  95   0 0.02
Thu 03/26 11Z 0.62 2332  88  95   0 0.02
Thu 03/26 12Z 0.61 2333  84  90   1 0.01
Thu 03/26 13Z 0.66 2435  83  81   2 0.01
Thu 03/26 14Z 0.73 2435  87  49   2 0.01
Thu 03/26 15Z 0.81 2533  89  29   2 0.01
Thu 03/26 16Z 0.77 2530  90  19   2 0.00
Thu 03/26 17Z 0.81 2527  89  33   2 0.00
Thu 03/26 18Z 0.86 2525  85  53   3 0.00
Thu 03/26 19Z 0.99 2425  83  71   3 0.00
Thu 03/26 20Z 0.94 2422  84  95   4 0.00
Thu 03/26 21Z 0.83 2318  86  96   4 0.01
Thu 03/26 22Z 0.62 2218  94  98   4 0.05
Thu 03/26 23Z 0.40 2119  97  99   5 0.13
Fri 03/27 00Z 0.50 2321  97  98   5 0.22
Fri 03/27 01Z 0.62 2521  98  94   5 0.17
Fri 03/27 02Z 0.48 2617  98  96   4 0.11
Fri 03/27 03Z 0.39 2615  99  97   4 0.09
Fri 03/27 04Z 0.33 2713  98  95   4 0.07
Fri 03/27 05Z 0.32 2814  98  96   3 0.08
Fri 03/27 06Z 0.29 3015  98  97   2 0.08
Fri 03/27 07Z 0.27 3015  97  94   2 0.07
Fri 03/27 08Z 0.29 3016  98  89   0 0.06
Fri 03/27 09Z 0.30 3117  97  90   0 0.05
Fri 03/27 10Z 0.34 3120  97  78  -1 0.03
Fri 03/27 11Z 0.33 3221  96  60  -3 0.02

Run total areal avg QPF for the greens is: 1.43 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