NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260822_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)
=== ===== === ==== ==== === === === ====
Sat 08/22 18Z 0.74 1309  91  30  10 0.00
Sat 08/22 19Z 0.51 1211  92  31  11 0.00
Sat 08/22 20Z 0.48 1213  91  35  11 0.00
Sat 08/22 21Z 0.50 1214  92  32  11 0.00
Sat 08/22 22Z 0.57 1217  90  32  11 0.00
Sat 08/22 23Z 0.45 1319  84  32  11 0.00
Sun 08/23 00Z 0.36 1320  84  28  12 0.00
Sun 08/23 01Z 0.25 1419  86  25  12 0.00
Sun 08/23 02Z 0.19 1419  88  23  12 0.00
Sun 08/23 03Z 0.17 1519  88  29  12 0.01
Sun 08/23 04Z 0.13 1518  87  43  12 0.00
Sun 08/23 05Z 0.08 1618  88  58  11 0.00
Sun 08/23 06Z 0.04 1617  90  64  11 0.00
Sun 08/23 07Z 0.04 1715  91  61  11 0.00
Sun 08/23 08Z 0.05 1713  92  60  11 0.00
Sun 08/23 09Z 0.04 1712  92  59  11 0.00
Sun 08/23 10Z 0.05 1612  92  61  12 0.00
Sun 08/23 11Z 0.09 1514  94  68  12 0.01
Sun 08/23 12Z 0.12 1515  95  78  11 0.01
Sun 08/23 13Z 0.15 1517  96  72  12 0.01
Sun 08/23 14Z 0.16 1517  96  61  12 0.01
Sun 08/23 15Z 0.13 1517  96  63  12 0.01
Sun 08/23 16Z 0.08 1615  96  62  12 0.01
Sun 08/23 17Z 0.03 1613  96  61  12 0.00
Sun 08/23 18Z 0.08 1513  94  61  13 0.00
Sun 08/23 19Z 0.06 1613  94  64  13 0.00
Sun 08/23 20Z 0.09 1714  97  67  13 0.00
Sun 08/23 21Z 0.11 1813  98  52  13 0.01
Sun 08/23 22Z 0.18 1814  97  38  13 0.01
Sun 08/23 23Z 0.27 1915  97  25  13 0.02
Mon 08/24 00Z 0.38 2016  98  15  12 0.02
Mon 08/24 01Z 0.55 2218  98  44  12 0.03
Mon 08/24 02Z 0.60 2317  94  47  12 0.04
Mon 08/24 03Z 0.70 2418  91  55  11 0.03
Mon 08/24 04Z 0.63 2518  90  49  11 0.00
Mon 08/24 05Z 0.58 2417  87  42  11 0.00
Mon 08/24 06Z 0.50 2416  82  51  11 0.00
Mon 08/24 07Z 0.47 2416  82  25  11 0.00
Mon 08/24 08Z 0.41 2316  78  12  11 0.00
Mon 08/24 09Z 0.40 2316  80  25  11 0.00
Mon 08/24 10Z 0.38 2315  82  34  10 0.00
Mon 08/24 11Z 0.37 2315  84  41  10 0.00
Mon 08/24 12Z 0.36 2215  86  49  10 0.01
Mon 08/24 13Z 0.36 2215  84  55   9 0.00
Mon 08/24 14Z 0.39 2215  84  64   9 0.00
Mon 08/24 15Z 0.41 2215  80  63   9 0.00
Mon 08/24 16Z 0.56 2215  81  71   9 0.00
Mon 08/24 17Z 0.75 2214  82  59   8 0.00
Mon 08/24 18Z 2.62 2212  84  35   8 0.00
Mon 08/24 19Z 4.52 2212  83  20   9 0.00
Mon 08/24 20Z 4.27 2211  81  26   9 0.00
Mon 08/24 21Z 2.48 2111  77  41   9 0.00
Mon 08/24 22Z 1.12 2112  79  49   9 0.00
Mon 08/24 23Z 0.73 2215  80  83   9 0.00
Tue 08/25 00Z 0.65 2218  83  78   9 0.02
Tue 08/25 01Z 0.88 2322  86  86   9 0.01
Tue 08/25 02Z 0.95 2425  95  80   9 0.01
Tue 08/25 03Z 0.81 2524  86  85   8 0.02
Tue 08/25 04Z 0.85 2425  84  86   8 0.00
Tue 08/25 05Z 0.83 2425  91  88   8 0.00

Run total areal avg QPF for the Central_Greens is: 0.30 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