NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260501_0600
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 05/01 06Z 0.29 3216  94  76  -2 0.00
Fri 05/01 07Z 0.30 3217  90  73  -2 0.00
Fri 05/01 08Z 0.31 3218  87  72  -2 0.00
Fri 05/01 09Z 0.33 3218  86  73  -3 0.00
Fri 05/01 10Z 0.37 3119  88  74  -3 0.00
Fri 05/01 11Z 0.41 3119  89  73  -3 0.00
Fri 05/01 12Z 0.41 3118  90  64  -3 0.00
Fri 05/01 13Z 0.51 3116  89  51  -4 0.00
Fri 05/01 14Z 1.66 3115  89  45  -4 0.00
Fri 05/01 15Z 2.95 3113  89  45  -4 0.00
Fri 05/01 16Z 3.05 3012  86  43  -3 0.00
Fri 05/01 17Z 3.40 2912  83  46  -3 0.00
Fri 05/01 18Z 4.11 2911  77  47  -2 0.00
Fri 05/01 19Z 4.79 2909  73  39  -1 0.00
Fri 05/01 20Z 4.74 2908  71  35  -1 0.00
Fri 05/01 21Z 3.66 2806  68  35   0 0.00
Fri 05/01 22Z 2.18 2804  65  33   0 0.00
Fri 05/01 23Z 0.59 2703  63  46   0 0.00
Sat 05/02 00Z 0.15 2201  61  57   0 0.00
Sat 05/02 01Z 0.14 2002  62  75   0 0.00
Sat 05/02 02Z 0.12 1903  63  82   0 0.00
Sat 05/02 03Z 0.08 1605  64  87   0 0.00
Sat 05/02 04Z 0.10 1507  66  95   0 0.00
Sat 05/02 05Z 0.17 1510  76  94   0 0.01
Sat 05/02 06Z 0.18 1413  93  96  -1 0.06
Sat 05/02 07Z 0.15 1514  98  95  -1 0.09
Sat 05/02 08Z 0.18 1712  99  89  -1 0.06
Sat 05/02 09Z 0.25 1911  99  83  -1 0.02
Sat 05/02 10Z 0.26 2109  99  80  -1 0.02
Sat 05/02 11Z 0.24 2207  99  76  -1 0.02
Sat 05/02 12Z 0.27 2307 100  77  -2 0.01
Sat 05/02 13Z 0.29 2508  99  67  -2 0.01
Sat 05/02 14Z 0.33 2609  99  62  -2 0.01
Sat 05/02 15Z 0.33 2810  98  56  -3 0.00
Sat 05/02 16Z 0.35 2911  96  51  -3 0.00
Sat 05/02 17Z 0.38 3012  94  43  -3 0.00
Sat 05/02 18Z 0.99 3111  92  38  -3 0.00
Sat 05/02 19Z 1.65 3109  89  32  -2 0.00
Sat 05/02 20Z 1.40 3108  88  33  -2 0.00
Sat 05/02 21Z 0.97 3106  86  27  -2 0.00
Sat 05/02 22Z 0.40 3205  83  36  -2 0.00
Sat 05/02 23Z 0.17 3304  84  54  -2 0.00
Sun 05/03 00Z 0.11 3205  89  65  -2 0.00
Sun 05/03 01Z 0.07 3306  93  61  -2 0.01
Sun 05/03 02Z 0.05 3408  94  55  -2 0.01
Sun 05/03 03Z 0.05 3409  90  62  -3 0.01
Sun 05/03 04Z 0.06 3411  89  70  -3 0.01
Sun 05/03 05Z 0.06 3413  89  64  -3 0.00
Sun 05/03 06Z 0.08 3415  86  54  -3 0.00
Sun 05/03 07Z 0.08 3417  89  42  -4 0.00
Sun 05/03 08Z 0.08 3419  89  38  -4 0.00
Sun 05/03 09Z 0.07 3419  91  36  -4 0.00
Sun 05/03 10Z 0.06 3419  88  43  -4 0.00
Sun 05/03 11Z 0.09 3420  83  45  -4 0.00
Sun 05/03 12Z 0.17 3320  82  45  -5 0.00
Sun 05/03 13Z 0.92 3319  79  45  -5 0.00
Sun 05/03 14Z 3.28 3218  73  47  -5 0.00
Sun 05/03 15Z 5.12 3218  65  44  -5 0.00
Sun 05/03 16Z 6.59 3118  62  43  -4 0.00
Sun 05/03 17Z 7.14 3118  61  49  -4 0.00

Run total areal avg QPF for the Central_Greens is: 0.35 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