Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260625_1800
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)
=== ===== === ==== ==== === === === ====
Thu 06/25 18Z 2.73 2306  79  50  11 0.00
Thu 06/25 19Z 2.50 2307  80  51  11 0.02
Thu 06/25 20Z 2.60 2309  79  56  11 0.04
Thu 06/25 21Z 1.64 2209  76  59  11 0.03
Thu 06/25 22Z 0.51 2209  74  62  11 0.03
Thu 06/25 23Z 0.31 2109  70  68  11 0.02
Fri 06/26 00Z 0.31 2109  68  80  11 0.00
Fri 06/26 01Z 0.28 2009  69  88  11 0.00
Fri 06/26 02Z 0.16 1909  72  94  11 0.00
Fri 06/26 03Z 0.10 1710  80  97  10 0.01
Fri 06/26 04Z 0.11 1713  85  97  10 0.03
Fri 06/26 05Z 0.14 1715  90  96  10 0.05
Fri 06/26 06Z 0.18 1717  95  95  10 0.09
Fri 06/26 07Z 0.12 1719  95  90  10 0.11
Fri 06/26 08Z 0.06 1719  96  89  10 0.06
Fri 06/26 09Z 0.09 1819  97  88  10 0.03
Fri 06/26 10Z 0.12 1920  98  83  10 0.03
Fri 06/26 11Z 0.22 2019  99  82  10 0.03
Fri 06/26 12Z 0.30 2116  97  78  10 0.03
Fri 06/26 13Z 0.35 2215  94  75  10 0.02
Fri 06/26 14Z 0.37 2214  97  69  10 0.01
Fri 06/26 15Z 0.35 2212  98  66  10 0.01
Fri 06/26 16Z 0.38 2410  98  64  10 0.01
Fri 06/26 17Z 0.44 2509  97  62  10 0.01
Fri 06/26 18Z 0.45 2608  96  58  11 0.01
Fri 06/26 19Z 0.45 2607  94  63  11 0.02
Fri 06/26 20Z 0.42 2607  93  66  11 0.12
Fri 06/26 21Z 0.43 2809  91  68  11 0.11
Fri 06/26 22Z 0.46 2812  92  68  11 0.11
Fri 06/26 23Z 0.41 2912  90  61  11 0.04
Sat 06/27 00Z 0.43 2912  91  53  11 0.01
Sat 06/27 01Z 0.41 2913  93  52  11 0.00
Sat 06/27 02Z 0.30 3010  92  47  11 0.01
Sat 06/27 03Z 0.30 2910  92  46  11 0.00
Sat 06/27 04Z 0.27 2909  93  48  11 0.01
Sat 06/27 05Z 0.26 3009  94  49  11 0.01
Sat 06/27 06Z 0.23 2908  92  51  11 0.00
Sat 06/27 07Z 0.21 3008  91  53  11 0.00
Sat 06/27 08Z 0.18 3007  92  54  11 0.00
Sat 06/27 09Z 0.16 3106  94  53  10 0.00
Sat 06/27 10Z 0.13 3105  93  55  10 0.00
Sat 06/27 11Z 0.07 3304  92  54  10 0.00
Sat 06/27 12Z 0.03 3503  91  53  10 0.00
Sat 06/27 13Z 0.05 3402  91  55  10 0.00
Sat 06/27 14Z 0.03 3301  91  57  10 0.00
Sat 06/27 15Z 0.04 3001  92  56  10 0.01
Sat 06/27 16Z 0.04 2900  93  56  11 0.02
Sat 06/27 17Z 0.06 2700  93  59  11 0.03
Sat 06/27 18Z 0.07 3001  93  58  11 0.04
Sat 06/27 19Z 0.06 3201  92  55  11 0.02
Sat 06/27 20Z 0.05 3502  91  52  11 0.02
Sat 06/27 21Z 0.05 3502  91  51  11 0.03
Sat 06/27 22Z 0.05 3502  91  52  11 0.03
Sat 06/27 23Z 0.06 0002  91  51  12 0.02
Sun 06/28 00Z 0.08 0303  91  50  12 0.02
Sun 06/28 01Z 0.07 0203  91  51  11 0.01
Sun 06/28 02Z 0.09 0303  91  52  11 0.01
Sun 06/28 03Z 0.10 0304  91  55  11 0.00
Sun 06/28 04Z 0.07 0204  91  56  11 0.00
Sun 06/28 05Z 0.06 0105  91  59  11 0.00

Run total areal avg QPF for the greens is: 1.38 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