NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260822_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 08/22 00Z 0.15 0304  75   9  10 0.00
Sat 08/22 01Z 0.23 0605  72   8  10 0.00
Sat 08/22 02Z 0.30 0706  73   8  10 0.00
Sat 08/22 03Z 0.30 0806  75   8  10 0.00
Sat 08/22 04Z 0.30 0907  77   8  10 0.00
Sat 08/22 05Z 0.29 1107  78   9  10 0.00
Sat 08/22 06Z 0.28 1208  78   9  10 0.00
Sat 08/22 07Z 0.25 1410  79  10  10 0.00
Sat 08/22 08Z 0.22 1511  79   8  10 0.00
Sat 08/22 09Z 0.24 1512  80   7  10 0.00
Sat 08/22 10Z 0.25 1613  78   7  10 0.00
Sat 08/22 11Z 0.31 1513  77   8  10 0.00
Sat 08/22 12Z 0.37 1414  79  10  10 0.00
Sat 08/22 13Z 0.45 1315  83  13   9 0.00
Sat 08/22 14Z 0.52 1317  84  17   9 0.00
Sat 08/22 15Z 0.62 1318  82  20   9 0.00
Sat 08/22 16Z 0.97 1417  81  20   9 0.00
Sat 08/22 17Z 1.20 1417  82  20  10 0.00
Sat 08/22 18Z 0.92 1416  82  19  10 0.00
Sat 08/22 19Z 0.70 1416  82  25  10 0.00
Sat 08/22 20Z 0.66 1415  81  30  10 0.00
Sat 08/22 21Z 0.59 1415  80  33  10 0.00
Sat 08/22 22Z 0.50 1416  80  37  11 0.00
Sat 08/22 23Z 0.41 1416  80  40  11 0.00
Sun 08/23 00Z 0.37 1417  80  41  11 0.00
Sun 08/23 01Z 0.38 1417  81  38  11 0.00
Sun 08/23 02Z 0.33 1418  83  40  11 0.00
Sun 08/23 03Z 0.25 1517  84  47  11 0.00
Sun 08/23 04Z 0.21 1517  85  55  12 0.00
Sun 08/23 05Z 0.17 1617  86  63  12 0.00
Sun 08/23 06Z 0.13 1615  86  70  12 0.00
Sun 08/23 07Z 0.12 1614  86  74  12 0.00
Sun 08/23 08Z 0.09 1612  87  79  12 0.00
Sun 08/23 09Z 0.08 1611  87  83  12 0.00
Sun 08/23 10Z 0.12 1510  87  86  12 0.00
Sun 08/23 11Z 0.16 1411  87  91  13 0.01
Sun 08/23 12Z 0.21 1413  88  93  13 0.01
Sun 08/23 13Z 0.24 1414  90  96  13 0.01
Sun 08/23 14Z 0.23 1413  90  95  13 0.01
Sun 08/23 15Z 0.21 1412  92  94  12 0.04
Sun 08/23 16Z 0.15 1511  95  92  12 0.16
Sun 08/23 17Z 0.13 1511  95  87  13 0.10
Sun 08/23 18Z 0.09 1612  97  84  13 0.04
Sun 08/23 19Z 0.06 1712  97  83  13 0.02
Sun 08/23 20Z 0.07 1810  96  76  13 0.00
Sun 08/23 21Z 0.06 1810  95  72  13 0.00
Sun 08/23 22Z 0.05 1810  93  62  14 0.00
Sun 08/23 23Z 0.07 1911  93  53  14 0.00
Mon 08/24 00Z 0.13 1913  93  45  14 0.00
Mon 08/24 01Z 0.19 2013  94  51  13 0.00
Mon 08/24 02Z 0.28 2115  96  65  13 0.02
Mon 08/24 03Z 0.31 2312  89  73  13 0.08
Mon 08/24 04Z 0.29 2410  83  68  13 0.01
Mon 08/24 05Z 0.27 2410  82  65  12 0.01
Mon 08/24 06Z 0.22 2309  81  50  12 0.00
Mon 08/24 07Z 0.20 2309  78  34  13 0.00
Mon 08/24 08Z 0.19 2209  77  26  12 0.00
Mon 08/24 09Z 0.20 2210  79  26  12 0.00
Mon 08/24 10Z 0.18 2110  80  25  12 0.00
Mon 08/24 11Z 0.18 2111  82  30  12 0.00

Run total areal avg QPF for the greens is: 0.52 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