NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260402_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)
=== ===== === ==== ==== === === === ====
Thu 04/02 00Z 0.05 3410  85  14  -2 0.00
Thu 04/02 01Z 0.06 0010  78   9  -1 0.00
Thu 04/02 02Z 0.10 0111  70  13  -1 0.00
Thu 04/02 03Z 0.14 0310  63  15   0 0.00
Thu 04/02 04Z 0.13 0507  54  17   0 0.00
Thu 04/02 05Z 0.11 0806  50  26   0 0.00
Thu 04/02 06Z 0.10 1106  52  58   0 0.00
Thu 04/02 07Z 0.07 1408  59  57   0 0.00
Thu 04/02 08Z 0.08 1409  71  56   0 0.01
Thu 04/02 09Z 0.08 1408  79  56   0 0.01
Thu 04/02 10Z 0.10 1309  84  40   0 0.01
Thu 04/02 11Z 0.11 1310  85  36   0 0.00
Thu 04/02 12Z 0.11 1311  87  41   0 0.00
Thu 04/02 13Z 0.09 1410  90  49   0 0.01
Thu 04/02 14Z 0.08 1409  91  42   0 0.00
Thu 04/02 15Z 0.09 1309  92  43   0 0.00
Thu 04/02 16Z 0.10 1308  91  52   0 0.00
Thu 04/02 17Z 0.12 1209  90  58   0 0.00
Thu 04/02 18Z 0.11 1309  89  63   0 0.00
Thu 04/02 19Z 0.10 1308  87  74   0 0.00
Thu 04/02 20Z 0.11 1310  86  87   1 0.00
Thu 04/02 21Z 0.11 1411  85  95   1 0.00
Thu 04/02 22Z 0.13 1414  85  97   2 0.00
Thu 04/02 23Z 0.11 1417  86  93   2 0.00
Fri 04/03 00Z 0.10 1519  86  76   2 0.00
Fri 04/03 01Z 0.08 1522  84  93   2 0.00
Fri 04/03 02Z 0.05 1622  86  90   3 0.00
Fri 04/03 03Z 0.03 1724  90  89   4 0.00
Fri 04/03 04Z 0.06 1725  95  80   4 0.01
Fri 04/03 05Z 0.09 1828  97  80   5 0.01
Fri 04/03 06Z 0.13 1830  97  80   6 0.01
Fri 04/03 07Z 0.19 1931  97  77   7 0.02
Fri 04/03 08Z 0.23 1933  97  83   8 0.02
Fri 04/03 09Z 0.29 2034  98  83   8 0.02
Fri 04/03 10Z 0.36 2037  98  76   9 0.03
Fri 04/03 11Z 0.41 2139  98  82  10 0.04
Fri 04/03 12Z 0.43 2138  97  83  10 0.02
Fri 04/03 13Z 0.47 2237  97  90  10 0.03
Fri 04/03 14Z 0.49 2336  96  83  11 0.05
Fri 04/03 15Z 0.56 2338  96  78  11 0.02
Fri 04/03 16Z 0.59 2437  95  66  11 0.01
Fri 04/03 17Z 0.63 2437  95  69  11 0.00
Fri 04/03 18Z 0.70 2437  94  88  11 0.01
Fri 04/03 19Z 0.77 2438  93  79  11 0.00
Fri 04/03 20Z 0.86 2537  91  68  11 0.00
Fri 04/03 21Z 0.97 2538  91  35  10 0.00
Fri 04/03 22Z 1.14 2539  93  11   9 0.00
Fri 04/03 23Z 1.21 2540  92  11   9 0.00
Sat 04/04 00Z 1.26 2542  95  15   9 0.01
Sat 04/04 01Z 1.28 2542  98  17   8 0.02
Sat 04/04 02Z 1.40 2641  98  13   8 0.03
Sat 04/04 03Z 1.53 2640  97  10   6 0.03
Sat 04/04 04Z 1.34 2736  97  10   5 0.03
Sat 04/04 05Z 1.06 2832  94  13   3 0.02
Sat 04/04 06Z 0.64 2828  87  13   3 0.01
Sat 04/04 07Z 0.43 2924  83  14   3 0.00
Sat 04/04 08Z 0.29 3021  84  16   3 0.00
Sat 04/04 09Z 0.19 3118  85  18   4 0.00
Sat 04/04 10Z 0.09 3214  85  19   4 0.00
Sat 04/04 11Z 0.04 3411  86  20   4 0.00

Run total areal avg QPF for the Central_Greens is: 0.49 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