NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260415_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)
=== ===== === ==== ==== === === === ====
Wed 04/15 00Z 0.82 2525  77  81  12 0.00
Wed 04/15 01Z 1.14 2631  87  78  11 0.02
Wed 04/15 02Z 1.03 2827  95  72  10 0.02
Wed 04/15 03Z 0.71 2923  97  51   9 0.03
Wed 04/15 04Z 0.55 2920  97  34   9 0.02
Wed 04/15 05Z 0.43 2919  96  29   8 0.01
Wed 04/15 06Z 0.36 2916  94  20   8 0.01
Wed 04/15 07Z 0.33 2917  92  16   8 0.00
Wed 04/15 08Z 0.31 2917  91  16   8 0.01
Wed 04/15 09Z 0.24 3016  85  13   9 0.01
Wed 04/15 10Z 0.19 3013  78  11  10 0.00
Wed 04/15 11Z 0.14 3011  71  15  11 0.00
Wed 04/15 12Z 0.14 2909  66  19  12 0.00
Wed 04/15 13Z 0.17 2810  64  19  12 0.00
Wed 04/15 14Z 0.17 2709  58  20  13 0.00
Wed 04/15 15Z 0.17 2408  54  17  13 0.00
Wed 04/15 16Z 0.27 2313  61  16  12 0.00
Wed 04/15 17Z 0.23 2113  56  80  12 0.00
Wed 04/15 18Z 0.29 2115  65  90  11 0.00
Wed 04/15 19Z 0.44 2117  78  90  11 0.00
Wed 04/15 20Z 0.62 2223  92  76  12 0.03
Wed 04/15 21Z 0.71 2422  91  66  12 0.00
Wed 04/15 22Z 0.75 2325  95  59  13 0.02
Wed 04/15 23Z 0.85 2525  95  70  12 0.01
Thu 04/16 00Z 0.84 2525  95  75  13 0.01
Thu 04/16 01Z 0.87 2525  93  80  12 0.01
Thu 04/16 02Z 0.87 2526  92  83  13 0.01
Thu 04/16 03Z 0.77 2624  90  85  13 0.00
Thu 04/16 04Z 0.79 2623  91  90  12 0.01
Thu 04/16 05Z 0.73 2622  92  96  12 0.01
Thu 04/16 06Z 0.70 2619  96  91  11 0.01
Thu 04/16 07Z 0.57 2616  97  91  11 0.01
Thu 04/16 08Z 0.54 2615  97  85  11 0.03
Thu 04/16 09Z 0.56 2716  97  89  11 0.04
Thu 04/16 10Z 0.52 2816  96  82  11 0.02
Thu 04/16 11Z 0.49 2716  95  78  10 0.01
Thu 04/16 12Z 0.49 2716  94  76  11 0.01
Thu 04/16 13Z 0.43 2614  93  65  11 0.00
Thu 04/16 14Z 0.39 2613  92  63  11 0.00
Thu 04/16 15Z 0.33 2610  91  61  11 0.00
Thu 04/16 16Z 0.37 2510  89  73  11 0.00
Thu 04/16 17Z 0.37 2409  86  79  11 0.00
Thu 04/16 18Z 0.53 2410  85  85  11 0.00
Thu 04/16 19Z 0.76 2311  87  75  11 0.00
Thu 04/16 20Z 0.94 2312  88  83  11 0.00
Thu 04/16 21Z 1.12 2315  89  84  12 0.00
Thu 04/16 22Z 0.94 2317  91  74  12 0.00
Thu 04/16 23Z 0.77 2416  89  69  12 0.00
Fri 04/17 00Z 0.70 2416  89  83  12 0.01
Fri 04/17 01Z 0.44 2412  92  91  12 0.09
Fri 04/17 02Z 0.24 2707  90  89  12 0.44
Fri 04/17 03Z 0.41 2613  91  94  11 0.29
Fri 04/17 04Z 0.23 2607  80  88  12 0.05
Fri 04/17 05Z 0.34 2510  78  92  12 0.00
Fri 04/17 06Z 0.43 2513  81  73  12 0.00
Fri 04/17 07Z 0.41 2613  84  77  12 0.01
Fri 04/17 08Z 0.38 2612  88  80  11 0.01
Fri 04/17 09Z 0.28 2608  91  85  11 0.01
Fri 04/17 10Z 0.16 2405  93  89  11 0.01
Fri 04/17 11Z 0.08 2102  94  94  11 0.01

Run total areal avg QPF for the Central_Greens is: 1.30 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