NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260719_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)
=== ===== === ==== ==== === === === ====
Sun 07/19 00Z 0.62 2327  95  87  15 0.00
Sun 07/19 01Z 0.87 2429  94  90  15 0.11
Sun 07/19 02Z 1.01 2530  96  75  14 0.12
Sun 07/19 03Z 1.05 2629  99  75  14 0.06
Sun 07/19 04Z 0.94 2725  98  76  13 0.08
Sun 07/19 05Z 0.96 2825  98  74  13 0.10
Sun 07/19 06Z 0.99 3028  98  46  11 0.08
Sun 07/19 07Z 0.81 3028  97  22  10 0.03
Sun 07/19 08Z 0.68 3130  96  13   8 0.03
Sun 07/19 09Z 0.59 3231  95  15   8 0.02
Sun 07/19 10Z 0.54 3231  94  18   7 0.02
Sun 07/19 11Z 0.53 3231  94  17   7 0.02
Sun 07/19 12Z 0.54 3230  94  14   7 0.02
Sun 07/19 13Z 0.56 3228  94  10   6 0.01
Sun 07/19 14Z 0.51 3226  91   7   7 0.01
Sun 07/19 15Z 0.53 3224  87   8   7 0.01
Sun 07/19 16Z 0.97 3123  84  11   7 0.00
Sun 07/19 17Z 5.43 3121  79  13   7 0.00
Sun 07/19 18Z 10.38 3020  75  12   7 0.00
Sun 07/19 19Z 11.92 3020  71  13   7 0.00
Sun 07/19 20Z 13.04 2921  68  13   8 0.00
Sun 07/19 21Z 12.84 3022  67  14   8 0.00
Sun 07/19 22Z 10.62 3023  67  15   8 0.00
Sun 07/19 23Z 4.90 3024  66  15   8 0.00
Mon 07/20 00Z 3.06 3125  68  18   8 0.00
Mon 07/20 01Z 2.38 3126  72  20   7 0.00
Mon 07/20 02Z 2.46 3126  77  18   7 0.00
Mon 07/20 03Z 1.46 3126  77  16   7 0.00
Mon 07/20 04Z 1.28 3126  76  15   7 0.00
Mon 07/20 05Z 1.18 3125  77  14   7 0.00
Mon 07/20 06Z 0.86 3223  78  12   7 0.00
Mon 07/20 07Z 0.66 3221  79  18   7 0.00
Mon 07/20 08Z 0.60 3220  82  24   7 0.00
Mon 07/20 09Z 0.53 3219  79  32   7 0.00
Mon 07/20 10Z 0.57 3219  77  29   7 0.00
Mon 07/20 11Z 0.55 3118  77  34   7 0.00
Mon 07/20 12Z 0.50 3116  75  39   8 0.00
Mon 07/20 13Z 0.54 3115  75  49   8 0.00
Mon 07/20 14Z 0.64 3011  75  43   8 0.00
Mon 07/20 15Z 1.67 2909  76  47   8 0.00
Mon 07/20 16Z 2.66 2808  76  49   8 0.00
Mon 07/20 17Z 3.52 2608  75  51   9 0.00
Mon 07/20 18Z 3.57 2507  76  49   9 0.00
Mon 07/20 19Z 3.23 2407  76  48  10 0.00
Mon 07/20 20Z 2.72 2308  76  48  10 0.00
Mon 07/20 21Z 1.72 2208  76  44  11 0.00
Mon 07/20 22Z 0.70 2209  73  38  11 0.00
Mon 07/20 23Z 0.36 2110  70  34  11 0.00
Tue 07/21 00Z 0.38 2113  65  30  12 0.00
Tue 07/21 01Z 0.36 2015  59  26  12 0.00
Tue 07/21 02Z 0.35 2017  58  25  12 0.00
Tue 07/21 03Z 0.39 2019  60  23  12 0.00
Tue 07/21 04Z 0.47 2121  59  21  12 0.00
Tue 07/21 05Z 0.52 2123  64  18  12 0.00
Tue 07/21 06Z 0.51 2123  65  17  12 0.00
Tue 07/21 07Z 0.47 2123  66  16  12 0.00
Tue 07/21 08Z 0.45 2123  62  14  12 0.00
Tue 07/21 09Z 0.41 2123  63  14  11 0.00
Tue 07/21 10Z 0.34 2023  70  14  11 0.00
Tue 07/21 11Z 0.34 2025  76  10  11 0.00

Run total areal avg QPF for the greens is: 0.72 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