NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260717_0000
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)
=== ===== === ==== ==== === === === ====
Fri 07/17 00Z 0.31 3220  80   5  11 0.00
Fri 07/17 01Z 0.44 3226  71   1  10 0.00
Fri 07/17 02Z 0.54 3228  65  11  10 0.00
Fri 07/17 03Z 0.55 3229  59  19  10 0.00
Fri 07/17 04Z 0.49 3229  55  25  10 0.00
Fri 07/17 05Z 0.44 3229  54  25   9 0.00
Fri 07/17 06Z 0.42 3227  53  20   9 0.00
Fri 07/17 07Z 0.46 3226  56  17   9 0.00
Fri 07/17 08Z 0.43 3225  59  13   9 0.00
Fri 07/17 09Z 0.41 3224  62  12   8 0.00
Fri 07/17 10Z 0.39 3224  65  12   8 0.00
Fri 07/17 11Z 0.33 3224  64  12   9 0.00
Fri 07/17 12Z 0.29 3223  64  15   9 0.00
Fri 07/17 13Z 0.26 3221  64  16   9 0.00
Fri 07/17 14Z 0.28 3218  62  18   9 0.00
Fri 07/17 15Z 0.29 3216  60  19   9 0.00
Fri 07/17 16Z 0.31 3215  56  21   9 0.00
Fri 07/17 17Z 0.57 3214  52  22   9 0.00
Fri 07/17 18Z 0.81 3113  52  22  10 0.00
Fri 07/17 19Z 1.13 3011  57  22  10 0.00
Fri 07/17 20Z 1.61 2910  61  22  10 0.00
Fri 07/17 21Z 1.69 2809  63  21  10 0.00
Fri 07/17 22Z 0.82 2809  61  17  11 0.00
Fri 07/17 23Z 0.56 2809  58  12  11 0.00
Sat 07/18 00Z 0.54 2709  55  10  11 0.00
Sat 07/18 01Z 0.50 2709  53  10  11 0.00
Sat 07/18 02Z 0.46 2708  52  10  11 0.00
Sat 07/18 03Z 0.41 2608  50  10  11 0.00
Sat 07/18 04Z 0.45 2509  50  10  11 0.00
Sat 07/18 05Z 0.42 2408  50  11  11 0.00
Sat 07/18 06Z 0.46 2409  51  15  11 0.00
Sat 07/18 07Z 0.46 2409  52  18  11 0.00
Sat 07/18 08Z 0.43 2309  54  15  11 0.00
Sat 07/18 09Z 0.43 2311  51  13  11 0.00
Sat 07/18 10Z 0.50 2314  47  29  12 0.00
Sat 07/18 11Z 0.57 2317  48  65  12 0.00
Sat 07/18 12Z 0.62 2319  56  76  12 0.00
Sat 07/18 13Z 0.62 2220  66  64  13 0.00
Sat 07/18 14Z 0.69 2221  75  49  13 0.00
Sat 07/18 15Z 0.84 2122  72  54  14 0.00
Sat 07/18 16Z 2.07 2123  70  69  15 0.00
Sat 07/18 17Z 3.30 2124  71  76  15 0.00
Sat 07/18 18Z 5.22 2024  71  80  16 0.00
Sat 07/18 19Z 3.79 2024  78  72  16 0.00
Sat 07/18 20Z 1.39 2031  92  90  15 0.08
Sat 07/18 21Z 0.73 2032  92  76  15 0.06
Sat 07/18 22Z 0.72 2033  97  72  15 0.01
Sat 07/18 23Z 0.66 2034  98  53  15 0.03
Sun 07/19 00Z 0.68 2133  98  65  16 0.03
Sun 07/19 01Z 0.68 2230  94  75  16 0.25
Sun 07/19 02Z 0.63 2324  83  62  16 0.69
Sun 07/19 03Z 0.71 2229  91  33  15 0.06
Sun 07/19 04Z 0.76 2529  93  21  15 0.01
Sun 07/19 05Z 0.73 2627  93  29  15 0.01
Sun 07/19 07Z 0.84 2726  98  61  13 0.02
Sun 07/19 08Z 0.90 2927  98  34  11 0.05
Sun 07/19 09Z 0.59 3027  95  11  10 0.05
Sun 07/19 10Z 0.48 3129  93  13   8 0.02
Sun 07/19 11Z 0.41 3129  91  17   8 0.01

Run total areal avg QPF for the Central_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