NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260412_1800
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)
=== ===== === ==== ==== === === === ====
Sun 04/12 18Z 0.19 1906  51  54  -1 0.00
Sun 04/12 19Z 0.22 1808  47  67   0 0.00
Sun 04/12 20Z 0.22 1811  47  79   0 0.00
Sun 04/12 21Z 0.07 1615  43  96   0 0.00
Sun 04/12 22Z 0.80 1817  50  89   0 0.00
Sun 04/12 23Z 0.58 1922  63  98   0 0.02
Mon 04/13 00Z 0.44 1925  85  98  -1 0.03
Mon 04/13 01Z 0.41 2026  89  99   0 0.05
Mon 04/13 02Z 0.42 2028  85  99   2 0.04
Mon 04/13 03Z 0.46 2131  84  98   3 0.05
Mon 04/13 04Z 0.45 2133  83  97   5 0.05
Mon 04/13 05Z 0.45 2134  87  97   7 0.04
Mon 04/13 06Z 0.51 2237  87  97   7 0.04
Mon 04/13 07Z 0.54 2239  87  80  10 0.01
Mon 04/13 08Z 0.62 2343  90  89  10 0.02
Mon 04/13 09Z 0.70 2443  93  87  10 0.02
Mon 04/13 10Z 0.74 2543  90  85  11 0.00
Mon 04/13 11Z 0.75 2542  87  80  11 0.01
Mon 04/13 12Z 0.73 2540  85  73  11 0.00
Mon 04/13 13Z 0.72 2538  84  62  11 0.00
Mon 04/13 14Z 0.69 2534  79  44  11 0.00
Mon 04/13 15Z 0.66 2432  78  50  11 0.00
Mon 04/13 16Z 0.79 2334  71  21  11 0.00
Mon 04/13 17Z 1.32 2336  85  90   9 0.02
Mon 04/13 18Z 1.38 2340  92  95   9 0.06
Mon 04/13 19Z 1.34 2342  97  96   9 0.05
Mon 04/13 20Z 1.30 2541  98  93   9 0.09
Mon 04/13 21Z 1.19 2639  98  80  10 0.04
Mon 04/13 22Z 1.26 2639  98  67  10 0.03
Mon 04/13 23Z 1.26 2738  97  66  10 0.03
Tue 04/14 00Z 1.30 2737  97  62   9 0.01
Tue 04/14 01Z 1.32 2737  98  60   9 0.02
Tue 04/14 02Z 1.25 2835  98  54   8 0.03
Tue 04/14 03Z 1.10 2831  97  53   8 0.02
Tue 04/14 04Z 0.85 2928  97  39   8 0.02
Tue 04/14 05Z 0.66 3025  97  33   7 0.02
Tue 04/14 06Z 0.51 3023  95  34   7 0.01
Tue 04/14 07Z 0.41 3021  92  35   8 0.01
Tue 04/14 08Z 0.36 3020  87  36   8 0.01
Tue 04/14 09Z 0.31 2918  80  30   9 0.01
Tue 04/14 10Z 0.30 2917  75  28   9 0.01
Tue 04/14 11Z 0.23 2913  69  21  10 0.00
Tue 04/14 12Z 0.24 2812  72  25   9 0.00
Tue 04/14 13Z 0.23 2611  69  25  10 0.00
Tue 04/14 14Z 0.22 2411  66  31  10 0.00
Tue 04/14 15Z 0.26 2314  67  43  11 0.00
Tue 04/14 16Z 0.35 2317  73  51  11 0.00
Tue 04/14 17Z 0.52 2420  85  68  10 0.00
Tue 04/14 18Z 0.38 2120  73  69  12 0.00
Tue 04/14 19Z 0.37 2022  76  69  13 0.00
Tue 04/14 20Z 0.50 2122  79  69  13 0.00
Tue 04/14 21Z 1.01 2223  85  71  12 0.05
Tue 04/14 22Z 1.08 2224  86  79  12 0.04
Tue 04/14 23Z 0.70 2323  94  85  12 0.22
Wed 04/15 00Z 0.99 2527  94  88  11 0.24
Wed 04/15 01Z 0.84 2726  94  87  12 0.09
Wed 04/15 02Z 0.82 2826  93  78  11 0.10
Wed 04/15 03Z 0.79 2724  93  68  11 0.02
Wed 04/15 04Z 0.79 2726  97  53  11 0.03
Wed 04/15 05Z 0.64 2823  96  36  11 0.02

Run total areal avg QPF for the Central_Greens is: 1.68 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