NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261004_1200
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 10/04 12Z 0.05 1717  90   5   4 0.00
Sun 10/04 13Z 0.06 1719  91   3   4 0.00
Sun 10/04 14Z 0.08 1620  91   4   4 0.00
Sun 10/04 15Z 0.08 1620  90  12   4 0.00
Sun 10/04 16Z 0.07 1619  89  23   4 0.00
Sun 10/04 17Z 0.08 1618  88  48   4 0.00
Sun 10/04 18Z 0.07 1717  88  88   4 0.00
Sun 10/04 19Z 0.08 1718  84  80   4 0.00
Sun 10/04 20Z 0.11 1717  79  91   4 0.00
Sun 10/04 21Z 0.13 1818  72  77   4 0.00
Sun 10/04 22Z 0.16 1819  66  53   5 0.00
Sun 10/04 23Z 0.16 1819  72  57   5 0.00
Mon 10/05 00Z 0.22 1919  81  53   6 0.00
Mon 10/05 01Z 0.27 2017  87  61   6 0.00
Mon 10/05 02Z 0.34 2117  93  39   6 0.00
Mon 10/05 03Z 0.41 2218  95  32   6 0.00
Mon 10/05 04Z 0.44 2318  95  31   6 0.00
Mon 10/05 05Z 0.44 2318  94  41   6 0.00
Mon 10/05 06Z 0.43 2418  91  48   7 0.01
Mon 10/05 07Z 0.45 2419  88  52   7 0.01
Mon 10/05 08Z 0.48 2420  86  41   8 0.01
Mon 10/05 09Z 0.62 2424  87  34   7 0.01
Mon 10/05 10Z 0.76 2427  91  41   7 0.01
Mon 10/05 11Z 0.95 2530  97  80   6 0.03
Mon 10/05 12Z 1.09 2629  91  72   4 0.07
Mon 10/05 13Z 1.01 2727  78  53   4 0.02
Mon 10/05 14Z 1.21 2728  80  38   3 0.01
Mon 10/05 15Z 1.71 2827  86  30   2 0.02
Mon 10/05 16Z 7.36 2827  84  26   1 0.01
Mon 10/05 17Z 8.74 2825  80  16   1 0.00
Mon 10/05 18Z 13.50 2826  74  13   0 0.00
Mon 10/05 19Z 12.15 2828  74  47   0 0.00
Mon 10/05 20Z 7.15 2828  81  52   0 0.00
Mon 10/05 21Z 3.16 2828  87  51  -1 0.00
Mon 10/05 22Z 1.65 2930  88  52  -1 0.00
Mon 10/05 23Z 1.41 2930  91  53  -2 0.00
Tue 10/06 00Z 1.25 2931  91  55  -2 0.00
Tue 10/06 01Z 1.16 2931  92  57  -3 0.00
Tue 10/06 02Z 1.12 2931  93  57  -3 0.00
Tue 10/06 03Z 1.03 3031  94  56  -3 0.00
Tue 10/06 04Z 1.04 2931  93  55  -4 0.00
Tue 10/06 05Z 0.97 2932  93  46  -4 0.00
Tue 10/06 06Z 0.86 3032  93  43  -4 0.00
Tue 10/06 07Z 0.73 3031  91  39  -4 0.00
Tue 10/06 08Z 0.66 3031  91  34  -3 0.00
Tue 10/06 09Z 0.62 3030  91  31  -3 0.00
Tue 10/06 10Z 0.54 3030  87  26  -3 0.00
Tue 10/06 11Z 0.50 3031  79  16  -2 0.00
Tue 10/06 12Z 0.44 3032  69  12  -1 0.00
Tue 10/06 13Z 0.37 3132  56   8   0 0.00
Tue 10/06 14Z 0.36 3130  51   5   0 0.00
Tue 10/06 15Z 0.41 3028  49   5   0 0.00
Tue 10/06 16Z 0.48 3026  47   1   0 0.00
Tue 10/06 17Z 0.62 3024  46   2  -1 0.00
Tue 10/06 18Z 1.08 2923  47   3  -1 0.00
Tue 10/06 19Z 7.33 2822  50   6  -1 0.00
Tue 10/06 20Z 10.33 2823  47  11  -1 0.00
Tue 10/06 21Z 4.12 2924  43  24  -1 0.00
Tue 10/06 22Z 1.66 2824  43  54   0 0.00
Tue 10/06 23Z 1.33 2925  42  59   0 0.00

Run total areal avg QPF for the Central_Greens is: 0.21 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